Other European officials and former U.S. officials said Pompeo's rise, if he is confirmed as secretary of state by the Senate, might have a more ambiguous effect on the negotiations and that, in any case, Trump's views are paramount.
"All our work is going into delivering a credible package that is sellable to Trump," said a European diplomat on condition of anonymity. "He is what matters here."
While Pompeo was a fierce critic of the deal, called the Joint Comprehensive Plan of Action (JCPOA), as a congressman, he tempered his views when testifying before Congress in January 2017 to seek confirmation as CIA director.
"Pompeo was a hawk on Iran. However, my understanding is he doesn’t want the deal to disappear," said a former senior U.S. official. "People should not jump to conclusions."
Many of Trump's top national security aides, like Tillerson, have argued that the United States is better off with the Iran nuclear deal than without it. That stance was echoed on Tuesday by the U.S. general who heads the U.S. military command responsible for the Middle East and Central Asia.
Former U.S. officials suggested that, as the administration nears a planned summit meeting with North Korean leader Kim Jong Un about Pyongyang's nuclear program, it could rethink its stance on the Iran deal.
European diplomats saw some chance Pompeo may have more influence over Trump than Tillerson, who antagonized the U.S. president by reportedly calling him a "moron" and who differed with Trump on Iran and other issues.
"If Pompeo is that hawkish, then in reality all it is is the affirmation of Trump’s policies. It’s Trump’s line," said a another European diplomat. "Hopefully he’ll have the mandate that Tillerson didn’t have."
