With slain Chicago teen Hadiya Pendleton's family looking on, Democrats and Republicans clashed Tuesday over the best ways to reduce gun violence while protecting citizens' Second Amendment rights.

In a packed hearing room, Illinois Sen. Dick Durbin, the Democratic chairman of the Senate Judiciary subcommittee, asked victims of gun violence to stand.

"Look about this room," Durbin said, as several dozen people stood up. "The debate we have before us has affected so many lives."

Standing in the second row were Pendleton's mother and father. The high school student was gunned down just weeks after she performed with classmates at President Barack Obama's inauguration. Her mother will watch the State of the Union with first lady Michelle Obama.

The hearing -- and the dozens of gun violence victims who have come to Capitol Hill to watch Obama's State of the Union address Tuesday evening -- are part of an ongoing effort to tighten the nation's gun laws after 20 elementary school children were killed in Newtown, Conn., in December. Obama and Vice President Joe Biden have made new laws a priority, but the package faces an uphill battle in Congress. Republicans have largely been silent on the issue, or have otherwise rejected the proposals.

"Constitutional rights are designed to be protected not just when they're popular but especially when passions are seeking to restrict and limit those rights," said Texas Republican Sen. Ted Cruz, who has emerged as a vocal critic of new gun laws.

Democrats have sought to maintain public pressure for new gun laws in the wake of Newtown. Sen. Richard Blumenthal, D-Conn., chastised a Wisconsin National Rifle Association lobbyist who told a local gathering that the NRA's agenda would be "delayed as the 'Connecticut effect' has to go through the process."

Blumenthal also published an opinion piece Tuesday calling the comments "callous and offensive."

During the hearing, Republicans sought to cast doubt on the effectiveness of gun control laws and questioned whether the government was prosecuting gun criminals using laws already on the books. Cruz and others also sought to cast doubts on the background check system; the NRA has opposed expanding background checks by requiring every gun buyer to have one.

That requirement is expected to be a centerpiece of any gun legislation. Judiciary Committee Chairman Patrick Leahy plans to start writing that bill later this month.

There is one area with more obvious agreement: gun trafficking. Under current law, trafficking in guns is often defined as little more than a paperwork violation, making it difficult for law enforcement to effectively prosecute people who buy guns and sell them to criminals.

At the hearing, Cruz expressed support for making trafficking a federal crime.

"I think all of us agree that if there are those that with criminal intent or transferring firearms to felons that there should be strict punishment for that. So that may be a productive area of cooperation," Cruz said.

Democrats pivoted quickly on Wednesday to make Mitt Romney the poster boy for the "Buffett Rule," the concept announced by President Obama during his State of the Union address that no millionaire should pay less than 30 percent in taxes on their income.

Democrats hope that Romney becomes a prime example of the excesses of the current tax structure. The linkage is meant not just to boost efforts to reform the tax code, but to also tarnish the former Massachusetts governor as a general election candidate by highlighting his wealth, and the restructuring work he did in the private sector to earn it.

One of Obama's chief re-election strategists admitted Wednesday that the release of Romney's tax returns on Tuesday, which showed that he paid about 14 percent in taxes on about $42 million of income in 2010 and 2011.

"Mitt may have thought story would be buried" by the State of the Union, Obama adviser David Axelrod wrote on Twitter, but "his tax release helped make case for Buffett rule."

The Buffett Rule, named for the billionaire investor who's pushed for higher taxes on the wealthy from their investment-related income, was a central part of Obama's speech on Tuesday. The address hit hard on the idea of fairness, and the idea that the tax code currently benefits the wealthy over middle class households.

"You can call this class warfare all you want," Obama said. "But asking a billionaire to pay at least as much as his secretary in taxes? Most Americans would call that common sense."

The administration seems especially confident in its position because the argument, when presented to voters, polls well.

A CBS News poll in December found that 60 percent of U.S. adults favor increasing taxes on households earning more than $1 million to help bridge the budget deficit. Mindful of that, Democrats sought to use a surtax on millionaires to finance a variety of components of the president's jobs bill when they came up for a vote last fall; all failed due to Republican objections.

On the more specific issue of dividend income, a New York Times/CBS News poll released this week found that a majority of Americans favor taxing it the same as income from employment.

In Romney, Democrats have a perfect poster boy for what they argue are the inequities in the current tax code. The former Massachusetts governor paid such a low tax rate because most of his income in recent years came from investment, which are taxed at a lower rate.

"Look at what we have with the disclosure of Mitt Romney and his tax returns -- an annual income of $21 million and a tax rate of less than 15 percent, about 14 percent," Illinois Sen. Dick Durbin, the second-ranking Senate Democrat, said Wednesday on Bloomberg Television. "And you ask yourself, now, is that fair? Is it fair that ... making that much money in a year is paying a lower rate tax rate than someone struggling paycheck to paycheck?"

And for much as the reignited tax debate has shone the spotlight on Romney and his wealth, it's allowed his Republican foes to pounce, as well.

"I think you have to live in a world of Swiss bank accounts and Cayman Island accounts and automatic $20 million-a-year income with no work to have some fantasy this far from reality," former House Speaker Newt Gingrich said at an Univision forum on Wednesday in Miami, connecting Romney's wealth to his position on illegal immigration.

Romney has emphasized that he pays all of the taxes required of him by law, and has pointed to the millions in additional income he and his wife donate to charity. But he characterized his tax burden as "fair" at Monday night's NBC News/National Journal/Tampa Bay Times debate, inserting himself into the narrative the Obama campaign is trying to build about inequality.

"I don’t think you want someone as the candidate for president who pays more taxes than he owes. So I’ll point out that that’s the case," he said. "And will there will discussion? Sure. Will it be an article? Yeah. But is it entirely legal and fair? Absolutely."

And that's why Democrats have no hesitance about linking Romney to the Buffett Rule, so much so that it might just be renamed after the former GOP governor.

"We agree with the president that it makes no sense that a millionaire should pay lower taxes than a secretary. So, it's a priority for us to act on some sort of Romney--" Sen. Charles Schumer (D-NY) said at a press conference Wednesday on Capitol Hill before catching himself, "--I mean, Buffett Rule this year."