Trump explained that he and Tillerson had disagreed on many topics, but the question of whether or not to stay in the Iran deal was one they hotly contended. “When you look at the Iran deal. I thought it was terrible. He thought it was OK,” Trump said. “I wanted to either break it or do something, he felt a little differently. So we were not really thinking the same.”

In two months, on May 12th, the US must have a decision regarding the fate of the Iran deal. It now appears likely that Trump has decided to drop out of the Joint Comprehensive Plan of Action (JCPOA). If that happens, the deal will be dead.

The JCPOA required Iran to surrender much of its nuclear infrastructure and allow international inspection in exchange for international sanctions relief. It was an agreement signed between Tehran and six world powers: Britain, China, France, Germany, Russia and the United States, who all still see it as a landmark victory in the battle to stop the spread of nuclear weapons.

During his campaign for the US presidency, Trump called the accord the “worst deal ever.” However, Tillerson and Defense Secretary Mattis urged Trump to listen to his European allies and to preserve the deal intact, while seeking new measures to pressure Iran. Now that Tillerson is gone, Trump will likely blow up the entire accord.

This could have catastrophic consequences for US national security, according to Thomas Countryman, who was assistant secretary of state for international security and nonproliferation from 2011 to 2017. Countryman says that Tillerson “served as a Cabinet-level check on some of President Trump’s worst impulses, such as wanting to ‘break’ the Iran nuclear agreement,” and adds that, “Mr. Pompeo instead favors an aggressive Middle East policy that would undo the diplomatic progress we made on nonproliferation and potentially embroil us in a new conflict in that region.”

Mark Dubowitz of the Foundation Foundation for Defense of Democracies tweeted, “For those Europeans (and Americans) who think Trump is not serious about walking away on May 12th if there’s no agreement to fix the Iran nuke deal, I give you Exhibit A: his soon-to-be Secretary of State Mike Pompeo.”

Tillerson’s chief of strategy, Brian Hook, will be meet with British, French and German officials in Berlin on Thursday to discuss efforts to reform the deal. Expanding the agreement to include restrictions on Iran’s ballistic missile program, and ending the “sunset clauses” that allow Tehran to resume some enrichment within 10 years will be among topics of discussion.

While European leaders agree with these ideas, they are looking at a possible “supplement” arrangement that would leave the core deal intact. It may not be possible, though, to go far enough to please Trump and Pompeo.

It has been reported that Israeli officials say that Trump opposes Europe’s “cosmetic changes” and wants a “significant” rewriting of the Iran deal itself, which is expected to shatter the agreement.