“We cannot prevent an Iranian nuclear bomb under the decaying and rotten structure of the current agreement,” Trump said, announcing that he would begin reinstating “U.S. nuclear sanctions on the Iranian regime” and at “the highest level of economic sanction.”

But leading Republican policy voices in Congress have distanced themselves from Trump’s position on Iran, including House Armed Services Chairman Mac Thornberry of Texas and House Foreign Affairs Chairman Ed Royce of California. Royce noted on Tuesday some of the deal’s concessions to Iran are irreversible, including returning roughly $50 billion in formerly frozen assets.

“Tearing up the nuclear deal will not recover this cash,” Royce said at a committee hearing on Iran. “That toothpaste isn’t going back into the tube. It also won’t help galvanize our allies into addressing Iran’s dangerous activities that threaten us all. I fear a withdrawal would actually set back these efforts. And Congress has heard nothing about [an] alternative.”

Thornberry said he would have preferred to give European allies a few more months to strengthen the deal. Nonetheless, he stressed that a “strong, international effort” is required to curtail Iran’s aggressive behavior.

“Now that the President has decided that the United States will withdraw, we must have two critical priorities,” he said in a statement. “One is to further enhance our own military capabilities. The other is to strengthen our alliances.”