The two Democrats to vote against the motion were Sens. Mark Pryor (AR) and Mark Begich (AK), both of whom are up for reelection next year.
"Americans are looking to us for solutions and for action, not filibustering or sloganeering," said Senate Judiciary Chairman Patrick Leahy (D-VT). "The Second Amendment is secure and will remain secure and protected."
Between Republican threats to use every procedural tool available to gum up the legislation -- the Senate provides many -- and skittish red-state Democrats facing reelection in 2014, the fate of the legislation is uncertain.
The bill got a boost Wednesday after Sens. Joe Manchin (D-WV) and Toomey announced a deal to expand mandatory background checks to gun shows and Internet firearm sales. But the National Rifle Association quickly came out against the compromise and later threatened to grade lawmakers based on how they vote on the final procedural motion and passage.
For now, Toomey and Kirk are the only Republicans to openly support the proposal.
"I think we've got a few voting hurdles, and I don't know how they're going to turn out," Toomey said Thursday morning on MSNBC. "I think we will be able to get started on the underlying bill with the vote today, but how the amendments play out -- I think it's just too early to know."
If the Republicans follow through on their threats to block or slow down the bill, the Senate may not be able to begin work on it until Friday or possibly next week. The Manchin-Toomey measure is expected to be brought as the first amendment to the base legislation filed by Senate Majority Leader Harry Reid (D-NV), who has promised opportunities for amendments.
The Republicans who voted to begin debate were Sens. Lamar Alexander (TN), Kelly Ayotte (NH), Richard Burr (NC), Saxby Chambliss (GA), Tom Coburn (OK), Susan Collins (ME), Bob Corker (TN), Jeff Flake (AZ), Lindsey Graham (SC), Dean Heller (NV), John Hoeven (ND), Johnny Isakson (GA), Mark Kirk (IL), John McCain (AZ), Pat Toomey (PA) and Roger Wicker (MS). Some of them signaled they may filibuster later.
"The legislation can still be filibustered after today in the United States Senate," said Graham, who voted for the motion to begin debate on the gun legislation. "And even if gun control legislation passes the Democratic-controlled U.S. Senate it is unlikely to pass the Republican-controlled House of Representatives."