With gun control legislation on the verge of stalling in Congress, President Obama traveled to Connecticut on Monday to campaign for stricter gun laws and to round up some powerful lobbyists to make his case on Capitol Hill this week.

Obama addressed an audience at the University of Hartford and then returned to Washington aboard Air Force One along with 11 relatives of the 26 victims gunned down in December at Sandy Hook Elementary School, about 50 miles from where the president was speaking.

The families this week hope to persuade lawmakers to approve new restrictions on guns, including a ban on many types of assault-style weapons, limits on ammo magazines and expanded background checks for gun purchasers.

The president's push for tighter gun laws faces increasing opposition among Senate Republicans, however, with a group of 13 lawmakers threatening to filibuster the legislation, blocking any chance for a vote.

"Some back in Washington are already floating the idea that they might use political stunts to prevent votes on any of these reforms," Obama told the Hartford crowd.

Congress has already killed off proposals to ban assault weapons and high-capacity magazines after both Republicans and red-state Democrats balked at supporting them. Expanded background checks may now be the only measure that stands a chance of passing both the House and Senate and as of Monday even that didn't have enough support to bring it to the floor for debate.

Senate Majority Leader Harry Reid, D-Nev., on Monday pledged to take up legislation that would expand background checks, but he would not provide any details on the timing.

Reid blamed lack of progress on the 13 Republicans, who say they will block any bill that restricts gun ownership, including a measure that widens background checks.

"Many Senate Republicans seem afraid to even engage in this debate," Reid said. "Shame on them."

Senate rules require 60 votes to end a filibuster and Democrats control only 53 seats.

A group of Republican senators -- including Rand Paul of Kentucky, Mike Lee of Utah, Ted Cruz of Texas and Marco Rubio of Florida -- on Monday renewed their threat to filibuster any bill "that will serve as a vehicle for any additional gun restrictions."

Republicans oppose broader background checks, they said, because they could restrict firearms transfers among hunters and family members. They also charge that broader background checks could lead to creation of a national registry of gun owners.

Sens. Pat Toomey, R-Pa., and Joe Manchin, D-W.Va., both of whom represent pro-gun states, are reportedly negotiating a last-minute measure to expand background checks in a way that would exempt close relatives and hunters. But pro-gun groups say the exceptions Toomey and Manchin propose aren't enough to win their support.

"It doesn't account for unmarried couples or same-sex couples," John Pierce, co-founder and spokesman for gun-rights group OpenCarry.org, told The Washington Examiner.