Sen. Joe Manchin, a conservative Democrat, has withdrawn his support for a new Iran sanctions bill after President Obama reiterated his threat to veto it in the State of the Union speech Tuesday night.

The president has repeatedly said any new threat of sanctions would derail the six-month interim deal to roll back parts of Iran's nuclear program that the U.S. and other world powers negotiated with Tehran.

Manchin, D-W.Va., faces a tough re-election this fall and has regularly parted ways with the administration on Obamacare and energy policy.

He initially backed the sanctions bill sponsored by Sens. Bob Menendez, D-N.J., and Mark Kirk, R-Ill., but yanked his support for it Tuesday night after Obama said, "For the sake of our national security, we must give diplomacy a chance to succeed."

None of the other 13 Democrats who have signed onto the bill as co-sponsors have followed suit as of Wednesday afternoon, according to a review of the legislation on

The bill allows a full year of diplomacy with Iran to play out before imposing new sanctions if Tehran failed to fulfill its obligations under the preliminary nuclear deal.

Manchin said he only supported the bill to strengthen the president's hand in negotiations, but now thinks it should not receive a vote on the Senate floor.

“I did not sign it with the intention that it would ever be voted upon or used upon while we’re negotiating,” he told MSNBC’s Chris Matthews.

“I signed it because I wanted to make sure the president had a hammer if he needed it and showed him how determined we were to do it and use it if we had to,” he added. “But with that being said, we’ve got to give peace a chance here, and we’ve got to support this process.”

If other Democrats follow Manchin's lead, the bill could be dead in its tracks. After the bill gained the backing of 59 co-sponsors, including more than a dozen Democrats in early January, Majority Leader Harry Reid, D-Nev., was under pressure to put it on the floor for a vote. Two weeks ago, Reid wouldn't commit to doing so, saying the Democratic caucus is deeply divided on the issue and he would see whether support for the measure gained ground or lost it over time.

The bill still maintains support from Menendez, the powerful chairman of the Foreign Relations Committee, 12 other Democrats and an overwhelming majority of Senate Republicans. But Manchin's reversal may create more momentum for a bipartisan compromise bill simply clarifying what Obama hopes to achieve in negotiations with Tehran.

In mid-January, Sen. Bob Corker of Tennessee, the top Republican on the Foreign Relations panel, said he suggested such a compromise bill during a closed-door meeting with Reid, several other key senators and Wendy Sherman, the undersecretary of state for political affairs.

“One of the things people are generally concerned about — even those who support the administration — is they want, I want, to see a negotiated settlement. I'm just worried that the administration has started this with an interim agreement that is so milquetoast, I mean, it's almost as if Iran has to do nothing, okay?” Corker told the Washington Examiner at the time.

Corker said a growing contingent of senators worry that the sanctions regime they helped build against Iran could “crater” as the talks proceed, and Tehran could have gained much-needed economic relief while making limited concessions that could easily be reversed in the six-month interim deal.