The Senate set a long-awaited vote for Wednesday on a bipartisan plan for expanding background checks to more firearms buyers, with supporters facing a steeply uphill path to victory.
By scheduling the roll call, Senate leaders ensured a showdown over the cornerstone of an effort by gun control supporters to tighten firearms laws following December's killings of 20 students and six aides at an elementary school in Newtown, Conn.
The Senate planned to vote on eight other amendments as well to a Democratic gun control bill that expands background checks, tightens laws against gun trafficking and boosts school safety aid.
They included Democratic proposals to ban assault weapons and high-capacity ammunition clips, a Republican proposal requiring states to honor other states' permits allowing concealed weapons and a broad GOP substitute for the measure.
Senate Majority Leader Harry Reid, D-Nev., and Minority Leader Mitch McConnell, R-Ky., announced their agreement to proceed on the votes beginning at 4 p.m. ET; all amendments will require 60 votes for passage.
A Senate Democratic leadership aide tells CBS News that even if the compromise background check amendment sponsored by Sens. Joe Manchin, D-W.Va. and Pat Toomey, R-Pa., fails, which is looking very possible, they could come back later with a new amendment on background checks, but the way forward after most of these amendments likely fail tomorrow is unclear.
Senate gun control supporters struggled Tuesday to salvage their drive to expand background checks to more buyers, buoyed by a visit from wounded former Rep. Gabrielle Giffords but facing enough potential opponents to derail their endeavor unless they can figure out how to win more votes.
No. 2 Democratic leader Richard Durbin of Illinois, his party's chief vote counter, left a lunch of Democratic senators saying they would need support from nine or 10 Republicans - a tall order. Subjecting more firearms transactions to the background checks now is the main thrust of the gun control effort launched after December's killings of 20 schoolchildren and six adults in Newtown, Conn.
Attending Tuesday's Senate lunch was Giffords, the Arizona Democrat severely hurt in a 2011 mass shooting in Tucson, and her husband, retired astronaut Mark Kelly. The two, gun owners both, have started a political committee that backs candidates who favor gun restrictions.
"His message was, `We've been through this,'" Durbin said, describing Kelly's remarks to the lawmakers. "`We're ready to fight back to stand up for those who have the courage to vote for gun safety.'"
Giffords did not address the lawmakers.