The odds are even worse in the GOP-led House, where only one Republican, Peter King of New York, has said he supports an assault weapons ban. That's fewer than the number of House Republicans who have raised the prospect of impeaching President Obama over his gun control efforts. (They are Steve Stockman and Louie Gohmert of Texas and Trey Radel of Florida.) House Speaker John Boehner, who could choose to simply not bring the bill up for a vote, said Tuesday that an assault weapons ban would give people "a false sense of security." In both chambers, the National Rifle Association has flexed its lobbying muscle in an effort to keep wavering pro-gun lawmakers from breaking ranks.

Mr. Obama called on Congress to pass the assault weapons and high-capacity magazine ban on Jan. 16, as well as a requirement for universal background checks for gun sales and other measures. Citing the horrific Newtown massacre one month earlier, the president said that "if there's even one thing we can do to reduce this violence, if there's even one life that can be saved, then we've got an obligation to try."

The White House opted not to send its own bill to Capitol Hill after Mr. Obama's announcement; it says it supports Feinstein's effort and has worked with her office in crafting the new version. Yet its hopes are likely pinned to what comes next: There are likely to be at least four pieces of major legislation introduced on gun control, according to a Democratic source, including a bill out of the Senate Judiciary Committee, which starts hearings on gun control next week. Reid seemed most optimistic about that measure, telling reporters, "It may not be everything everyone wants, but I hope it has stuff that is really important."

If a gun control measure is going to get through Congress, it would likely combine the most popular proposals of gun control advocates - including universal background checks, which is backed by more than nine out of 10 Americans according to CBS News/New York Times polling - with moves to improve mental health screenings, which has been the focus of some Republicans. (Those who are following the debate closely would consider a ban on high-capacity magazines, backed by 63 percent of Americans, perhaps the biggest possible victory for gun control advocates.) With more than half of Americans saying they support an assault weapons ban, however, backers of the bill introduced today aren't giving up.

"I thought for sure, after Virginia Tech, we would get something done," said McCarthy. "Aurora. But something happened in Newtown. The people of America said, 'How could this happen? How could this happen to our children?'"

She added that Americans should not listen to arguments that nothing can be done to save lives, stating that roughly 1,000 people have been killed guns since Newtown.

"I'm telling you it can be done," she said. "I'm telling you with all my heart it can be done."