A bipartisan Senate proposal to expand background checks on gun purchases is in jeopardy the day before a possible vote.
The bill, unveiled by Sen. Joe Manchin (D-W.Va.) and Pat Toomey (R-Pa.) last week, did not have the 60 votes needed to pass the chamber as of this afternoon, The Hill reported.
More from GlobalPost: Senators propose background checks for online gun sales, at gun shows
Three Democratic senators say they don't support it. Others have not committed their support.
Manchin and Toomey spent most of the day yesterday lobbying wavering colleagues, and today brought in former Rep. Gabby Giffords, injured in a 2011 shooting, and her husband Mark to try to whip votes.
The bill would extend criminal background checks to online and gun-show sales.
More from GlobalPost: Gun rights group breaks with NRA to support background checks
It's seen as President Barack Obama's best hope for meaningful gun control legislation in the wake of the Newtown massacre that left 20 children and six adults dead in December.
But the National Rifle Association is vehemently opposed to the bill, and has threatened to "punish" any conservatives who vote for it. Many Republicans leaders are also against it.
To appease some undecided rural-state senators, Manchin and Toomey may add language that would exempt far-flung communities in Alaska and North Dakota from some of the bill's requirements, Senate aides told the Washington Post.