WASHINGTON ― A Republican Senator who has advised President-elect Donald Trump on foreign policy said the U.S. should not immediately exit the Iran nuclear agreement.

Senate Foreign Relations Committee Chairman Bob Corker (R-Tenn.) was a forceful opponent of the nuclear accord when it was finalized in 2015, and was part of a unanimous Republican vote against the agreement. But the Congressional effort to kill the nuclear deal ultimately failed. Now, Corker says, the best option for the U.S. is to vigorously enforce the agreement that required Iran to dramatically scale back its nuclear infrastructure in exchange for sweeping sanctions relief.

Trump has characterized the nuclear accord as the “worst deal ever negotiated.” Last year, he vowed to tear it up. But at other times throughout the campaign he also promised to aggressively enforce the agreement. That inconsistency has left Iran-watchers uncertain about the future of the accord, which nuclear experts characterized this week as a “strong bulwark against an Iranian nuclear-weapons program.”

Corker, who was considered as a contender for both vice president and secretary of state in the Trump administration, said he believes that the next president would continue to uphold the agreement. “To tear it up on the front end, in my opinion, is just not going to happen,” he told reporters on Friday at a breakfast hosted by The Christian Science Monitor.

To abruptly exit the international agreement, backed by the United Kingdom, France, Germany, China, and Russia, would create an international crisis and the U.S. would bear the blame, Corker said.

“The Iran deal, from my perspective was flawed,” he said. “At the same time, because so much was given up on the front end, you’ve got a choice. You can come in and figuratively tear it up … and you can create a crisis on the front end by doing so. Or, you can understand that we have lots of challenges to deal with around the world … and what you can do instead is begin to radically ensure that it’s being implemented properly.”

Corker has indicated in the past that he favors enforcing rather than scrapping the nuclear agreement. But on Friday he also conceded that the accord is currently an effective constraint on Iran’s nuclear program.

“In spite of all the flaws in the agreement, nothing bad is going to happen relative to nuclear development in Iran over the next few years,” he said.