Democrats today cinched the 41 votes needed to filibuster the Republican-led effort to send a rejection of the Iran nuclear agreement to President Barack Obama’s desk.

Democratic Sens. Richard Blumenthal of Connecticut, Gary Peters of Michigan, and Ron Wyden of Oregon announced their backing of the accord Tuesday, garnering the support needed to prevent a resolution of disapproval from making it to the White House.

But according to Politico, it’s not clear if the 41 Democrats will stick together and actually filibuster the disapproval legislation later this week.

Indeed, some of the president’s fellow Democrats who have announced their support for the Iran deal have promised to allow an up-or-down vote on the disapproval resolution.

Also today, Sen. Joe Manchin, D-W.Va., broke from the majority in his party, announcing his opposition to the agreement.

Iran has shown no signs of changing its “deplorable” behavior, Manchin said in a statement, specifically in its long history of sponsoring terrorism, and the accord “does nothing to guarantee” a shift in the regime’s actions.

He said the estimated $100 billion Tehran will receive in sanctions relief under the agreement will be used in part to continue funding terrorism, further destabilizing the region.

He also expressed concerns of cheating, adding that if Iran violates the accord, he has “grave doubts that we will have unified, committed partners willing to prevent Iran from obtaining a nuclear weapon.”

Manchin is the fourth Democrat to reject the deal, joining Sens. Chuck Schumer of New York, Bob Menendez of New Jersey, and Ben Cardin of Maryland.

Sen. Maria Cantwell of Washington is the only Democratic senator still undecided.

All 54 Republicans are expected to reject the accord.

Congress reconvenes Tuesday and has until Sept. 17 to vote on the deal.