Early in the day, Sen. Johnny Isakson (R-GA) told CBS he won't filibuster the bill.
In the Capitol, Sens. John McCain (R-AZ) and Lindsey Graham (R-SC) reaffirmed that they'll vote to begin debate on the bill. Sen. Tom Coburn told TPM he'll also vote for the motion to proceed to debate. Sens. Kelly Ayotte (R-NH), Dean Heller (R-NV) and Susan Collins (R-ME) similarly told reporters they won't filibuster debate on the legislation.
"I do not understand -- it's incomprehensible to me that we would not move forward with debate and amendments on an issue this important to the American people," said McCain.
"My hope is that we can have a full and open debate with amendments, and if that occurs then I will certainly vote to proceed," said Collins.
The willingness of these Republican senators to begin debate has made Senate Democratic leaders confident that they can swiftly bring their bill to the floor, and continue courting GOP support while they debate the proposals.
But it's unclear whether the same GOP senators will also vote to end debate and permit a final up-or-down vote if the legislation that emerges is not to their liking. That, combined with the likely defections on an up-or-down vote of at least some red-state Democrats up facing reelection next year, means leaders may yet face an uphill battle to pass a final bill with background checks if they fail to secure Republicans support.
At least fourteen GOP senators have vowed to filibuster debate on any gun control bill.
Collins also signaled openness to voting for a proposal on expanded background checks being negotiated between Sens. Joe Manchin (D-WV) and Pat Toomey (R-PA).
"I do feel strong that we cannot do anything that would create a national registry of gun owners," Collins told reporters. "But I don't believe the language that's been drafted by Senator Manchin and Senator Toomey would end in that result."
Sens. Richard Burr (R-NC) and Max Baucus (D-MT) told TPM they were undecided on whether to block debate from beginning on the gun legislation.
Additional reporting by Benjy Sarlin