Rick Santorum suspends his 2012 presidential campaign at an event in Gettysburg, Pa.

Updated 3:02 p.m. - Former Pennsylvania Sen. Rick Santorum suspended his campaign on Tuesday, clearing Mitt Romney’s path to the Republican presidential nomination.

Citing weekend reflection with his family, prompted in part by a hospital stay for his youngest daughter, Santorum suspended his campaign, effective today.

"Ladies and gentleman, we made the decision to get into this race at our kitchen table against all the odds," Santorum said in remarks to reporters in Gettysburg, Pa.

"We made a decision over the weekend that while this presidential race for us is over for me and we will suspend our campaign effective today. We are not done fighting."

The announcement effectively stifles opposition to Romney from within the GOP; amid signs that the Republican establishment has started to rally around Romney, the former Massachusetts governor no longer faces any serious conservative challenger.

Former House Speaker Newt Gingrich and Texas Rep. Ron Paul remain active candidates, though neither of them have a plausible path to winning the 1,144 delegates needed to secure the nomination.

The decision comes two weeks before the Pennsylvania presidential primary. Santorum had faced the prospect of an embarrassing loss to Romney that threatened to short-circuit any of his future political aspirations, either statewide or nationally.

Slideshow: Rick Santorum's political life

A look at the Pennsylvania politician — his career on Capitol Hill and his White House aspirations.

Launch slideshow

Santorum’s announcement also follows the second health scare of the year for his daughter Bella who suffers from the chromosomal disorder Trisomy 18.

RELATED: What 'suspending' a campaign means

However, the former senator also huddled with conservative supporters recently to mull whether a path forward for his campaign truly existed. As recently as April 3, when he lost the Wisconsin primary to Romney, Santorum vowed to press forward, and described the race for the nomination as only having reached “halftime.”

Still, the course of the primary campaign meant a remarkable political resurrection for Santorum since his landslide defeat in 2006, when he sought a third term in the Senate. His presidential campaign offered a path to political redemption that had been unthinkable, even as recently as the end of last year.

Santorum called Romney earlier today to relay news of his decision.

"Senator Santorum is an able and worthy competitor, and I congratulate him on the campaign he ran. He has proven himself to be an important voice in our party and in the nation," Romney said in a written statement following Tuesday's announcement. "We both recognize that what is most important is putting the failures of the last three years behind us and setting America back on the path to prosperity."

First Read: Santorum's surprising ride

From non-factor to Iowa victor
Santorum was a non-factor in the campaign for most 2011 until a last-minute surge in Iowa, where he had traveled more than any other candidate.

The former Pennsylvania senator had done the first nominating state the “traditional” way, having traveled to all 99 of Iowa’s counties.

Still, a series of candidates – Rep. Michele Bachmann, Texas Gov. Rick Perry, Herman Cain and former House Speaker Newt Gingrich – had taken turns surging to the top of the polls in the Hawkeye State before Santorum got his boost, in late December, on the eve of the state’s caucuses.

Santorum battled Romney to a virtual tie in Iowa before the state’s Republican Party crowned Romney the apparent winner by a slim, eight-vote margin.

It wasn't until Jan. 21 – the day of the South Carolina primary – that the Iowa GOP reversed itself due to unaccounted votes and declared Santorum the actual winner of the caucuses. By then, Romney had steam-rolled his opponents to win the New Hampshire primary, and Gingrich had re-emerged as the leading conservative challenger to Romney in the Palmetto State.

Santorum re-emerged as Romney’s biggest threat on Feb. 7, when he stunned the front-runner by winning contests in Minnesota, Colorado and Missouri.

Santorum as chief Romney alternative
Santorum’s victories in those states again laid bare fissures in the Republican Party over Romney’s candidacy. The most conservative elements of the party appeared unwilling to line up behind Romney. And with Gingrich fading in the aftermath of an onslaught of negative advertising in Florida, Santorum again claimed the mantle of chief Romney alternative. 

The emergence of a supportive super PAC – the Red, White and Blue Fund – helped Santorum make his case. Much of that group’s financing came from investor Foster Friess.

The turning point in the Santorum-Romney battle came in at the end of February.  Rather than skip the primary in Michigan – the state where Romney was raised and where his father had been an iconic Republican governor – Santorum decided to take his battle to Romney’s home turf.

The campaigning turned heavily on issues of class, and Santorum emphasized his commonness with the state’s hard-hit working and middle classes.

He was aided by Democratic-led efforts to remind voters of Romney’s opposition to the 2009 bailouts of General Motors and Chrysler, along with Romney’s own missteps (among them, a highly-touted address to a cavernous Ford Field).

But Santorum also found himself the victim of tough ads launched by Romney and Restore Our Future, the pro-Romney super PAC.

The former senator was also dogged by questions about hot-button social issues, including contraception – a subject that was at the center of an intense national debate over women’s health issues.

Romney eventually eked out a three-point victory of Santorum, but carried momentum from Michigan (and Arizona, where he won a primary the same day) into Super Tuesday’s slate of 10 contests on March 6. There, Romney used the same strategy he had in Michigan to win six of the states, including Ohio, where Santorum had also sought to challenge Romney.

But Santorum was again able to beat back Romney, who gained some separation from his challengers in the delegate count after Super Tuesday, by way of winning Mississippi and Alabama’s primaries. Romney campaigned fleetingly in the states, but the deep conservatism of both states tilted the contests toward Santorum.

The Gingrich factor
Those primaries also made clear, though, that Gingrich’s continued presence in the race had eaten into Santorum’s support among conservatives.

Backers of the former senator started demanding Gingrich’s exit from the race, but the former House speaker defiantly vowed to continue with his campaign through the Republican convention this summer in Tampa.

All the while, Romney continued to amass delegates by winning caucuses and primaries in far-flung U.S. territories.

And it was one U.S. territory, Puerto Rico, where Romney finally trounced Santorum, despite the ex-senator having campaigned there. He subsequently paraded into Illinois, where he won the March 20 primary in the Land of Lincoln.

Romney’s decisive win in Illinois prompted many national party leaders who had remained neutral – former Florida Gov. Jeb Bush, Florida Sen. Marco Rubio and Wisconsin Rep. Paul Ryan, among others – to get off the fence and endorse Romney in hopes of hastening the end of the primary campaign.

Santorum persevered through the April 3 primaries in D.C., Maryland and Wisconsin, then left the campaign trail when his daughter was admitted to the hospital last week.

The ex-senator was reflective in his remarks announcing the suspension of his campaign.

"Miracle after miracle, this race was as improbable as any race you'll ever seen for president," he said, referencing the 11 states and millions of votes won over the course of his campaign. He made no mention of Romney.

Romney still faces token opposition in his march to formalize the nomination. Both Gingrich and Santorum signaled that they would continue – for now – with their campaigns in the aftermath of Santorum's announcement.

"I am committed to staying in this race all the way to Tampa so that the conservative movement has a real choice.  I humbly ask Senator Santorum’s supporters to visit Newt.org to review my conservative record and join us as we bring these values to Tampa," said Gingrich, whose persistence in the race had divided votes with Santorum in some pivotal contests.

Paul's campaign manager said that the Texas congressman would "plan to continue running hard" through the August convention in Tampa.

Susan Walsh / AP

President Barack Obama speaks before the National Governors Association, Monday, Feb. 27, 2012, in the State Dining Room of the White House.

The last time a Democratic presidential candidate won Arizona was 16 years ago, when Bill Clinton carried it in 1996.

The time before that? More than half a century ago, when Harry Truman won the state.

But as Republicans compete in their own primary there today, President Barack Obama's re-election team also has its eye on Arizona, a state where a growing Hispanic electorate and a deep divide on immigration policy could potentially help the president collect a much-needed 11 electoral votes in November.

A win there would be a reach, however. A recent NBC/Marist poll put Obama's approval rating in the state below 40%, and it showed him trailing most of the Republican presidential candidates there.

While Obama -- who didn't contest Arizona four years ago -- lost it by eight percentage points in 2008, his team believes that Sen. John McCain's less-than-double-digit victory in his own home state did much to lay bare Republicans' vulnerability there.

And, four years later, Obama's opponent is likely to face a much harsher reception from the state's growing Latino electorate than McCain, whose push for comprehensive immigration reform nearly derailed his candidacy early in the GOP primary.

From vows to veto the DREAM Act to heavy courtship of controversial endorsers like Arizona's Maricopa County Sheriff Joe Arpaio, GOP candidates' language on immigration has prompted public worry from Republican Hispanic groups as well as from party leaders like former Gov. Jeb Bush.

In Arizona, which became ground zero for the immigration debate after its 2010 passage of legislation that would give police broad authority to detain suspected illegal residents, Democrats have a favorite noun to describe Republican rhetoric on the matter.

"Overreach."

"I can't underscore enough our sense on the ground is that Republicans have overplayed their hand in terms of rhetoric and legislating immigration law," says Phoenix-based Democratic strategist Barry Dill. "And there's a backlash."

Those working to turn the state blue were thrilled to hear Mitt Romney call Arizona's stringent SB 1070 immigration measure "a model" for the nation's policies during a Feb. 22 debate in Mesa. They believe that kind of language -- underscored by Romney's endorsement on Sunday by Gov. Jan Brewer, who signed the bill into law -- could further mobilize Arizona voters looking for more moderate solutions to the immigration issue.

Harnessing that feeling on the ground will be the task of the campaign's substantial Arizona field operation.

The re-election campaign has three field offices already in Arizona -- in Phoenix, Tucson and Flagstaff -- and another set to open in heavily Hispanic Glendale in the coming weeks. The campaign says that staff and volunteers have held almost 500 voter registration sessions and more than 200 phone banks since the spring. Much of that effort is focused on the Hispanic community, with events held at Hispanic supermarkets and weekly Spanish- and English-language phone banks targeting Latinos. The campaign recently hired a Mexican-American regional field director.

While Team Obama hasn't yet invested in paid media there, the DNC has aired TV advertisements, including a six-day anti-Romney buy last year.

With the number of voting age Hispanic citizens growing by a whopping 85% last decade, per Census data, the benefits of such a focus are obvious. But the lift may still prove to be a heavy one.

The NBC/Marist Arizona survey this month also found that 51% of Hispanics approve of the president's performance, with 34% disapproving and 15% unsure.

Compare that to the 2008 numbers: Obama won 56% of the Latino vote in Arizona compared to McCain's 41%.

Luis Heredia, the executive director of the Arizona Democratic Party, estimates that Obama would have to boost that number to at least 65% in November to get over the finish line.

And Dill, who served as deputy state director for the Clinton/Gore win in 1996, puts that number even higher, at 68%.

He added that Democrats must be careful in 2012 to tailor their message to a diverse Hispanic community, saying that the party stumbled in past elections by treating the group as a single monolithic block.

"A big part of it had been our fault as campaign managers, as leaders," Dill said. "We had sort of homogenized the Hispanic community in Arizona into one group. And they're not, they're very diverse."

This year, Democrats say there's plenty of reasons to be optimistic.

Obama's team points to Democrats' double-digit mayoral victories in Tucson and Phoenix last year as well as the recall of Arizona State Senate president and author of SB 1070.

And Heredia adds that downballot races, like the one to replace retiring Rep. Gabby Giffords, will help build excitement for activists locally.

"I gain more and more confidence every day," he said.