"Officially, only three Republican senators — Toomey, Collins and Mark Kirk (Ill.) — have said they plan to vote for the Manchin-Toomey agreement. Democratic aides say the bill will need the backing of at least six Republican senators to pass. The [broader gun] measure still has a long and tortuous path, with dozens of amendments expected. The Senate is scheduled to begin formal debate Tuesday by first considering the plan to expand the gun background-check program."
According to The Associated Press, a vote on the Manchin-Toomey proposal could come as soon as Wednesday. Even with the uncertainty, it's seen as the most likely proposal to pass among a series of measures that include a proposed ban on assault-style weapons and high-capacity ammunition magazines.