Democratic senators said lawmakers may yet reach a compromise on expanded background checks for firearms sales, while Republicans said they wouldn't support extending rules to gun shows or private sellers.

"There is a sensible compromise that we can reach on background checks," Sen. Richard Blumenthal, a Connecticut Democrat who has pushed for tighter controls since the mass shooting at an elementary school in his state, said on CNN's State of the Union. "That unspeakable tragedy, I think, created an unstoppable momentum. History is on our side."

Almost four months after the mass shooting at Sandy Hook Elementary School in Newtown, Conn., prospects for President Obama's gun-safety agenda have faded amid opposition in Congress and waning public enthusiasm for several of the initiatives.

Last week, Obama sought to revive momentum, urging lawmakers to pass legislation to expand background checks on gun buyers, to ban civilian sales of military-style assault rifles, and to limit the ammunition capacity of magazines.

Senate leaders have ruled out the assault-weapons ban and magazine limits. Sen. Charles Schumer (D., N.Y.) said he was working with pro-gun lawmakers to write background-check language acceptable to both sides. "It's very hard," he said on NBC's Meet the Press. "We're working hard."

Sen. Lindsey Graham (R., S.C.) said on CNN that legislation that would require background checks on all gun buyers "is going nowhere."

Graham said that a more extensive system would not have prevented the Dec. 14 killing of 20 children and six educators at Sandy Hook Elementary School.

"Nothing we're talking about would have prevented Newtown from happening," Graham said. "The guy did not fail a background check."