"Those two leaders stepping up is a very good way to start," said Sen. Mary Landrieu, D-La., who is seeking re-election next year and has stressed her support for both the right to bear arms and reducing gun bloodshed. "How it ends, I don't know."
Toomey said Thursday he believes supporters of the proposal that he and Manchin have advanced will be able to beat back any filibuster attempt. "Beyond that, I just don't know yet," he said in a nationally broadcast interview hours before the critical vote.
"The problems that we have are not law-abiding gun owners like Joe and myself," Toomey said on "CBS This Morning."
But he conceded, "There's no panacea here."
In December, a gunman killed 20 first-graders and six staffers at Sandy Hook Elementary School in Newtown, Conn. Relatives of some victims were at the Capitol pressing lawmakers to back gun restrictions, and were holding a vigil outside the building where they were reading the names of recent victims of gun violence.
Expanded background checks are the core of the Democratic gun control drive. Other top proposals — including bans on assault weapons and high-capacity ammunition magazines — will be offered as amendments during Senate debate but seem destined for defeat.
The compromise between Toomey and Manchin, both owners of guns and "A'' ratings from the NRA, was likely to improve the prospects that the Senate might expand background checks by attracting broader support. But debate could last weeks and it was not known what amendments to the overall bill, either constricting or expanding gun rights, senators might approve.
Neither Toomey nor Manchin predicted the Senate would approve gun legislation and each said his vote on final passage would depend on what the measure looked like when debate ends. Manchin said he would vote against the overall legislation if his compromise with Toomey was defeated.