Senate Democrats, trying to simply hold their ranks together behind a background check amendment written by Senators Manchin and Toomey met for an emotional luncheon on Tuesday. Mr. Manchin gave a tearful, impassioned appeal for his measure as former Representative Gabrielle Giffords of Arizona looked on. Senator Tim Kaine, Democrat of Virginia, retold in detail the story of the professor at Virginia Tech who threw his body in front of a door to save students during the massacre there in 2007.

“It was really dramatic and convincing,” said Senator Amy Klobuchar of Minnesota.

Most legislative battles are fought with one party on offense, the other on defense. On guns, both parties see an opportunity to press their agendas, pursuing opposite goals and battling over the votes of the same conservative Democrats and moderate Republicans. In 1999, after the Columbine High School shootings, the Senate voted to expand federal background checks to purchases at gun shows, only to see a bipartisan coalition in the House vote to loosen existing background check rules. The legislation ultimately died.

The same dynamic could be developing this time. Republicans, increasingly confident that they will be able to sustain a filibuster on expanded background checks, have turned their attention to their own priorities, especially a conceal-and-carry measure being drafted by Senator John Cornyn of Texas.

Under that measure, any state with a conceal-and-carry rule would have to recognize the permit of any other state. Only Illinois and Washington, D.C., prohibit concealed weapons.

But while some state standards are low, other states maintain restrictive rules on concealed weapons and grant local law enforcement officials latitude to deny such permits, as they do in New York City, said Jonathan Lowy, the director of the legal action project at the Brady Center, a gun control group. The Cornyn amendment would allow a gun owner in Texas to carry his firearm in Times Square. Gun control advocates say the Cornyn measure would foster a race to the bottom, as gun owners in more restrictive states argue that they should not be held to standards that visitors are not held to.

Advocates see no difference between that rule and regulations that make each state recognize driver’s licenses from all other states, and it will almost certainly be backed by a number of Democrats. In 2009, a similar measure received 58 votes, including those of 20 Democrats, 13 of whom are still in the Senate. That was two votes short of the 60 needed for passage.