Washington (CNN) - Supporters of a bipartisan compromise to expand background checks for guns sales currently don't have the 60 votes they will need to win approval of their amendment so a vote on the proposal - which was expected midweek - is unlikely before the end of the week, Sen. Joe Manchin, D-West Virginia, told CNN in an exclusive interview Monday.
The vote is being pushed back so Manchin and others can build support for the controversial plan.
"We've got to work hard don't we," Manchin said, acknowledging he would need to convince a large number of undecided senators to support the measure which is opposed by the National Rifle Association. "We've got to work hard and the more people know about the bill, the more people read the bill, the more people see the facts of the bill, it breaks down all the misnomers."
He said he was reaching out to senators who voted last week against beginning debate on guns.
"We're working on all of them. Some of them who might not have voted for cloture might be more receptive once they see the facts," he said. "Now that we have gun groups coming out in support, it really helps us."
Asked if the vote would take place Tuesday or Wednesday, as supporters have hoped, Manchin said he didn't think so.
"I would say by the end of the week, probably. I really do," he said.