To a greater extent than he did in his first inaugural address four years ago, in his speech Monday President Barack Obama made a point of focusing attention on issues vital to specific constituencies within his winning coalition.

Obama’s inaugural theme four years ago was the need for national unity and his call for “a new era of responsibility, a recognition on the part of every American that we have duties to ourselves, our Nation, and the world.” And in his address Monday, Obama again included calls for unity, or what he called “collective action.”

But he went beyond that by, for the first time in a presidential inaugural address, referring explicitly to gay rights and to an event in gay rights history, the 1969 riot outside the Stonewall Inn, a gay bar in Greenwich Village in New York City. The Stonewall Inn protests followed a police raid on the bar and helped launch the gay rights movement.

Related: Obama takes ceremonial oath, tells nation 'our journey is not complete'

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President Barack Obama speaks during swearing-in ceremonies on the West front of the Capitol in Washington, Jan. 21, 2013.

In a statement issued after Obama’s victory last November, the Human Rights Campaign, the leading gay rights advocacy group, said, “HRC and our energized supporters have raised or contributed more than $20 million to re-elect President Obama and to advance marriage equality and other electoral priorities this (2012) cycle.”

In his address, Obama called for states to give legal recognition to marriage by same-sex couples: “Our journey is not complete until our gay brothers and sisters are treated like anyone else under the law – for if we are truly created equal, then surely the love we commit to one another must be equal as well,” he said.

Slideshow: 57th Presidential Inauguration

The major action on this issue will not come from Obama or Congress but from the Supreme Court, which on March 26, 2013 will hear oral arguments in two cases that will decide whether a state can define marriage as the union of one man and one woman. Also, the high court will decide whether a section of the 1996 Defense of Marriage Act, which defines marriage as solely between one man and one woman, violates the constitutional rights of same-sex couples.

Obama linked the Stonewall protests to the 1848 women’s rights convention in Seneca Falls, N.Y., and the 1965 voting rights march in Selma, Ala.

“We, the people, declare today that the most evident of truths – that all of us are created equal – is the star that guides us still; just as it guided our forebears through Seneca Falls, and Selma, and Stonewall … .”

Obama also acknowledged issues important to feminists, to people barred from voting by voter identification laws, and to immigrants illegally present in the United States who hope Congress this year will pass a law creating a process allowing them to become legal residents.

Calling for equal pay for men and women, he said, “Our journey is not complete until our wives, our mothers, and daughters can earn a living equal to their efforts.”

On voting rights, he said, “Our journey is not complete until no citizen is forced to wait for hours to exercise the right to vote.”

And on immigration, Obama said that he and Congress must “find a better way to welcome the striving, hopeful immigrants who still see America as a land of opportunity” and change the law so that “bright young students and engineers are enlisted in our workforce rather than expelled from our country.”

Referencing what’s likely to be a major legislative battle of the next several months, Obama alluded to his call for greater restrictions on the purchase of guns in the aftermath of the Dec. 14 shooting at Sandy Hook Elementary School, saying, “Our journey is not complete until all our children, from the streets of Detroit to the hills of Appalachia to the quiet lanes of Newtown, know that they are cared for, and cherished, and always safe from harm.”

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Earlier in the address he reiterated a theme from his 2009 inaugural address, urging Congress to take steps to remedy the effects of catastrophic weather events and global climate change.

“We will respond to the threat of climate change, knowing that the failure to do so would betray our children and future generations,” he said. “Some may still deny the overwhelming judgment of science, but none can avoid the devastating impact of raging fires, and crippling drought, and more powerful storms.”

Applauding this part of the speech, Frances Beinecke, president of the Natural Resources Defense Council, said, “This is a call to action against the climate chaos that is sweeping our nation and threatening our future. Now it's time to act. Power plants are our single largest source of carbon pollution. We must cut that pollution.”

The crucial arena for action on this issue may not be Congress but the Environmental Protection Agency. While the House did pass cap-and-trade carbon emissions legislation when the Democrats had the majority in 2009, the prospects for such legislation now seem doubtful at best. The Republican-led House is likely to keep a skeptical eye on additional subsidies for alternative energy technologies, although Congress did enact an extension of the Production Tax Credit for wind and other renewable electricity projects as part of the tax bill Obama signed into law on Jan. 2.

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President Barack Obama is sworn in by Supreme Court Chief Justice John Roberts as First lady Michelle Obama and daughters, Sasha Obama and Malia Obama look on during the public ceremonial inauguration on the West Front of the U.S. Capitol on Jan. 21, 2013.

Updated 4:33 p.m. — President Barack Obama issued a call to unity in his second inaugural address, urging the nation to move past the divisions that marked the last four years in politics and complete the work of living up to America's founding principles.

The president, in a speech that blended together post-partisan rhetoric and policy declarations, highlighted the progress made during his first term to end foreign wars and turn around the economy.

But Obama said that there was much unfinished work ahead, and he used Monday's speech to urge political leaders to finally rise above bitter squabbling — a recurring theme of his first term, and a mark of how difficult it has been for Obama to live up to his 2008 vow to change Washington's business as usual.

"Our journey is not complete," Obama said during one refrain in his speech.

Related: The full text of President Barack Obama's inaugural address

"We cannot mistake absolutism for principle, or substitute spectacle for politics, or treat name-calling as reasoned debate," Obama said. "We must act, knowing that our work will be imperfect.  We must act, knowing that today’s victories will be only partial, and that it will be up to those who stand here in four years, and forty years, and four hundred years hence to advance the timeless spirit once conferred to us in a spare Philadelphia hall."

Obama and Vice President Joe Biden were sworn in by Chief Justice John Roberts and Supreme Court Associate Justice Sonia Sotomayor, respectively, shortly before noon; Monday's oath of office was ceremonial, following their formal, constitutionally-prescribed swearing-in on Sunday.

Monday's ceremonies coincided with the federal holiday honoring Martin Luther King, Jr. Obama nodded to the slain civil rights leader during his speech, and the nation's first African-American president used one of King's Bibles during today's inauguration.

The president's speech, though, strode between acknowledging the accomplishments of his first term and the new priorities for his second. The president begins his new term this week intent upon pursuing an ambitious agenda following his decisive re-election victory last November over Republican opponent Mitt Romney.

Related: First Thoughts: Obama's second term begins

Rebuilding the economy, strengthening entitlement programs for future generations and addressing the threat of climate change were among the initiatives upon which the president touched during his speech. Obama nodded toward other priorities, that were set to define his next four years in office: equal rights for gay and lesbian Americans, immigration reform that offers undocumented residents a pathway to citizenship and new rules to curb gun violence.

But as political leaders from both parties looked on from the inaugural platform, Obama avoided much of the hard-charging rhetoric of last year's campaign.

Romney, the erstwhile GOP nominee, spent Inauguration Day at his home in La Jolla, Calif., and a former aide told NBC News it was unlikely that the former Massachusetts governor would watch today's festivities.

Wisconsin Rep. Paul Ryan, Romney's running mate last fall, said today was not a day to emphasize partisan divisions.

"But today, we put those disagreements aside," Ryan said in a statement. "Today, we remember what we share in common."

To be sure, a variety of bruising political battles between Obama and Congress — in particular, a House of Representatives controlled by Republicans — loomed on the horizon. On Wednesday, Republicans said, they would vote on a measure to extend the nation's debt limit by a few months.

Earlier in the day, Obama and the first family attended a service at St. John's Episcopal Church — the "Church of the Presidents," as it is sometimes known — just two blocks from the White House.

There, Dr. Luis Leon, the rector of the church, led a series of "prayers for the nation," Washington Cardinal Donald Weurl led a Gospel reading, and an Alexandria, Va., rabbi offered a final blessing. Biden and his wife also attended the service.

Former Presidents Bill Clinton and Jimmy Carter were among the dignitaries in attendance during the oath-of-office ceremonies during late Monday morning. Celebrities including musician Jay-Z and actress Eva Longoria joined government officials on the inaugural platform, and attendees were treated to performances by the Brooklyn Tabernacle Choir, Beyonce, Kelly Clarkson and James Taylor.

Obama retreated to a traditional luncheon on Capitol Hill following the inaugural ceremonies before participating in the parade down Washington's Pennsylvania Avenue.

"I recognize that democracy is not always easy, and I recognize there are profound differences in this room," Obama said in a toast before a bipartisan group of lawmakers, "but I just want to say thank you for your service and I want to thank your families for their service, because regardless of our political persuasions and perspectives, I know that all of us serve because we believe that we can make America for future generations."

Afterward, the president and first lady entered the motorcade from the Capitol and back to the White House, leaving the presidential motorcade at moments to walk for a portion of the trip.

The president and first lady will make their way to glitzy, black-tie inaugural balls later this evening before wrapping the whirlwind day of festivities.

NBC's Peter Alexander contributed to this report.

Slideshow: Obama's first term

Robin Buckson / AP

The president's first four years at the White House in pictures.

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Just 11 weeks removed from a sweeping re-election victory, President Barack Obama has hit the ground running with an ambitious second-term agenda that includes tackling the mounting national debt, immigration and gun control.

But the window in which the president has any hopes of meeting his aggressive goals has already begun to close.

Confronting the fading effectiveness of a second-term presidency, dogged opposition from Republicans in Congress and unexpected hurdles that will inevitably arise over the next four years, Obama must act with a sense of urgency on his plans, particularly amid the fiscal cliff negotiations.

“Second-term presidents generally get eight months or so ... where there's a honeymoon to push an agenda,” said James Thurber, the director of Center for Congressional and Presidential Studies at American University. “He doesn't even have a month.”

Newly armed with “Organizing for Action” – the remnants of the president’s campaign structure, converted to a nonprofit for advocacy purposes – Obama has suggested he will indeed act quickly on his top priorities.

But the next few months might well test the limits of the political capital that the president won in November, which saw Obama score a decisive victory over Republican opponent Mitt Romney and Democrats add seats in the House and the Senate.

If this past December’s lame duck Congress – in which Obama won higher tax rates for the wealthy, but only after a bitter fight with Republicans – offers any lessons, it’s that the GOP is equally committed to pursuing its own priorities, making compromise just as elusive as before.

The fiscal cliff fight will extend into this spring, when the government hits a series of major deadlines to keep the government funded and prevent a default on the national debt. That bare-knuckled fight could make or break Obama’s hopes of accomplishing much else on his agenda.

“I don't believe that he can wait until the last minute to deal with the debt ceiling and sequestration,” said Martin Frost, a former Democratic congressman from Texas. “That's got to be worked out during February.”

That fight would threaten to consume much of the political oxygen in Washington in any normal year. And Obama’s ability to pivot toward his other major priorities, gun violence and immigration, may well hinge upon how quickly and cleanly he can dispense with this spring’s spending fight.

History suggests that many presidents cannot hope to accomplish much in the last two years of their term, when the jockeying for the next presidential campaign begins. And with midterm elections looming in 2014, lawmakers will inevitably turn at some point from governing to politicking.

"There's kind of an arc of achievement in presidential administrations. Usually the first few months of a new administration is where most of the accomplishment takes place," said Ross Baker, a presidential historian at Rutgers University. "It's hard to imagine getting another piece of legislation of the magnitude of the Affordable Care Act in the second term."

And Obama’s hopes of significant reforms to immigration and gun laws might well depend upon how well (or how poorly) the spending fight with Congress proceeds.

The president last week laid out a series of measures intended to curb gun violence, most significantly proposals to limit the size of ammunition magazines, ban assault weapons and require universal background checks on firearm purchases. That plan won little praise from Republicans, and Obama might have to lean upon any reservoir of goodwill he has left after the spending fight to reach his goals.

Obama is practically obligated to attempt immigration reform after soothing the Latino community during last year’s election about his inability to follow through with a pledge to accomplish immigration reform in his first term. If re-elected, Obama told Hispanic voters, he would make immigration reform a priority in this second term.

Both proposals could engender significant Republican resistance, a phenomenon familiar to any observers of Obama’s first four years in office.

Another significant – and unpredictable – variable that could ruin even the best-laid plans involves the unknown crises that will inevitably arise during Obama’s second term.

A foreign policy crisis could always erupt and consume the president’s attention. Uprisings in Egypt, Libya and Syria, for instance, proved to major developments during Obama’s first four years in office.

If anything, the president’s first term offered a cautionary tale of how difficult it can be to navigate the obstacles to success that can arise.

The president nearly saw his signature health reform law go down to defeat after the advent of the Tea Party movement, for instance.

And external events – a near-meltdown of the economy, mass shootings, the Gulf of Mexico oil spill and other crises – consumed as much of the president’s first term as anything else.

Just as foreign policy could prove to be a diversion from policy making, it’s one of the few policy areas where a lame-duck president can leave a legacy.

For instance, Bill Clinton, in the waning days of his presidency, concentrated on achieving an elusive peace deal between Israelis and Palestinians.

“He's got a whole range of things on his plate right now,” Frost said of Obama, “it just really depends on how he prioritizes things.”

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President Barack Obama gets a hug from his daughter Malia as wife Michelle and daughter Sasha looks on in the Blue Room of the White House in Washington, Jan. 20, 2013.

President Barack Obama was officially sworn in Sunday for his second term as president of the United States, ahead of Monday's public events.

In a small and succinct ceremony at the White House, Obama recited the constitutionally mandated oath of office for the third of four expected times during his time in office.  

Embracing his children after the oath, his younger daughter Sasha was heard to whisper “good job, Daddy!” 

"I did it!" he responded, before she observed "You didn't mess up." 

Sunday's official swearing-in, administered by Chief Justice John Roberts, was the 57th inauguration of a president in American history. 

Wearing a dark suit and blue tie, Obama repeated the directive to “preserve, protect, and defend the Constitution of the United States." He was joined by First Lady Michelle Obama and his daughters Sasha and Malia.  

After thanking Roberts and waving to cameras, Obama and the first family left the White House's Blue Room. He will deliver his public inaugural address Monday on the west front of the United States Capitol.

During the brief swearing-in Sunday, the first lady -- who wore a dark blue dress -- held the family Bible upon which Obama laid his hand to swear the oath. According to inaugural officials, the Bible was a gift from Mrs. Obama’s father to his mother in 1958.

When Obama first took the oath of office on Jan. 20 four years ago, he and Chief Justice John Roberts tripped up over the wording, raising concerns about whether the constitutional requirements were fulfilled to the letter of the law.  Roberts went to the White House the next day and administered it again in full. 

The short Sunday ceremony was held because the constitutionally mandated inauguration date of Jan. 20 falls on a Sunday, so Obama will take the oath a fourth and final time on Monday before hundreds of thousands of observers on the National Mall. 

The Monday ceremonies will include the president's inaugural address, a luncheon with the president and members  of Congress and the traditional inaugural parade and balls. 

Ahead of the ceremony, the Obama family attended church at the Metropolitan African Methodist Episcopal Church in Washington , a historic place of worship that also hosted pre-inaugural services for former President Bill Clinton and Vice President Albert Gore.

Vice President Joe Biden was officially sworn in at about 8:20 a.m. ET Sunday.

The small weekend ceremonies for both men are a bit of a historical quirk, although today's swearing-in was the seventh in history to take place on a Sunday.  The last instance occurred in 1985, when President Ronald Reagan was formally sworn in for his second term in office.

Beginning with the second inauguration of Franklin D. Roosevelt in 1937, new presidents and vice presidents have been sworn in on Jan. 20 due to the changes laid out in the 20th Amendment to the Constitution.

(Before that, inaugurations were typically held on March 4, as directed by the 12th Amendment. But controversy over the length of the lame duck period forced that ceremony to be moved up by law).

Slideshow:

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Festivities for President Barack Obama's second inauguration.

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RELATED: More Inauguration Day content from NBCPolitics.com

In addition, eight vice presidents have been administered the oath of office upon the death of a president. The hastily planned ceremonies have taken place in hotels, homes and -- famously, after the death of John F. Kennedy -- aboard Air Force One. 

The oath of office for the president is set out in the Constitution.

Article II, Section 1, states as follows "Before he enter on the execution of his office, he shall take the following oath or affirmation: -- "I do solemnly swear (or affirm) that I will faithfully execute the office of president of the United States, and will to the best of my ability, preserve, protect, and defend the Constitution of the United States."

Traditionally, two minor changes are made. First, the president taking the oath says his name after the first word ("I, Barack Hussein Obama"). And second, the phrase "so help me God" is added at the end. 

NBC's Pete Williams and Shawna Thomas contributed to this report. 

Joe Biden was sworn in to a second term as the Vice President of the United States on Sunday morning, taking his oath from Associate Justice Sonia Sotomayor -- the first Hispanic in American history to administer an oath of office.

Biden personally selected Sotomayor, who is also the fourth woman to administer an oath, to conduct the brief ceremony at the vice president's residence at the Naval Observatory in Washington, D.C. 

By law, the president and vice president must be sworn in on Jan. 20. Because that date falls on a Sunday this year, both men take their formal oaths today, but will hold the traditional longer public ceremony tomorrow. 

Biden's swearing-in was originally scheduled to be held shortly before the president's, near noon Sunday. But Sotomayor's previous commitment to a book signing in New York City prompted officials to move the event earlier in the day. 

"It's an incredible honor to have Associate Justice Sonia Sotomayor swear me in," Biden said in a statement. "I believed strongly that she would make a great Justice, and it was one of the greatest pleasures of my career to be involved in her selection to the Court.  From the first time I met her, I was impressed by Justice Sotomayor's commitment to justice and opportunity for all Americans, and she continues to exemplify those values today. Above all, I'm happy for the chance to be sworn in by a friend - and someone I know will continue to do great things."

After the short swearing-in, Biden again thanked Sotomayor personally, explaining to the small group of guests the reason for the early timing of the event. 

Biden took the oath on a family Bible bearing a Celtic cross. It has been in the Biden family since 1893.

Cabinet members attending the ceremony included Attorney General Eric Holder and Interior Secretary Ken Salazar. He was joined on stage by his family, including wife Dr. Jill Biden and his three children. 

Georgia-based Pastor Louie Giglio, who was announced to deliver the benediction at President Obama's inauguration, will no longer be participating.

This comes after the liberal blog ThinkProgress reported that Giglio delivered an apparently anti-gay sermon.

An example from the sermon:

We must lovingly but firmly respond to the aggressive agenda of not all, but of many in the homosexual community. … Underneath this issue is a very powerful and aggressive moment. That movement is not a benevolent movement, it is a movement to seize by any means necessary the feeling and the mood of the day, to the point where the homosexual lifestyle becomes accepted as a norm in our society and is given full standing as any other lifestyle, as it relates to family.

Obama's inaugural committee today released this statement:

"We were not aware of Pastor Giglio's past comments at the time of his selection and they don't reflect our desire to celebrate the strength and diversity of our country at this Inaugural. Pastor Giglio was asked to deliver the benediction in large part for his leadership in combating human trafficking around the world. As we now work to select someone to deliver the benediction, we will ensure their beliefs reflect this administration's vision of inclusion and acceptance for all Americans."

The widow of civil rights icon Medgar Evers will deliver the invocation at President Barack Obama's second inauguration, the Presidential Inaugural Committee announced Tuesday.

Myrlie Evers-Williams, who headed the NAACP from 1995-1998, fought tenaciously for justice for her husband, the famed Mississippi activist killed in the driveway of their home in 1963. The man immediately suspected of murdering Evers was convicted and sentenced to life in prison in 1994, more than three decades after the crime.

"I am humbled to have been asked to deliver the invocation for the 57th inauguration of the President of the United States—especially in light of this historical time in America when we will celebrate the 50th Anniversary of the Civil Rights Movement,” she said in a statement. “It is indeed an exhilarating experience to have the distinct honor of representing that era."

In 2009, Obama chose Rev. Rick Warren to give the invocation, causing some outcry from the left because of Warren's opposition to same-sex marriage.

The president's formal inauguration will be held privately on Sunday, January 20, as dictated by law. But the ceremonial swearing-in -- where Evers-Williams will give the invocation -- will take place on Jan. 21, coinciding with Martin Luther King Jr. Day.

The Inaugural Committee also announced Tuesday that Rev. Louie Giglio, an Atlanta pastor and founder of youth faith movement Passion Conferences, will deliver the benediction at the ceremony.