Iranian diplomats reportedly studied President Donald Trump’s negotiating style and The Art of the Deal before high-level talks with Vice President JD Vance in Switzerland, trying to understand when Trump was signaling policy and when he was using threats as pressure.

The preparation was tested at the Bürgenstock resort near Lucerne, where Iranian parliament speaker Mohammad Bagher Ghalibaf, who led Iran’s negotiating team, was meeting Vance. During the talks, an aide reportedly entered the room with an urgent message: Trump had just threatened Iran over Hezbollah in Lebanon.

“Iran must immediately stop their highly paid PROXIES in Lebanon from causing trouble. If they don’t, we’ll hit Iran very hard again, just like we did last week, only harder!!!” Trump wrote.

Ghalibaf used the post against the talks themselves. According to Iranian and Israeli reports, he told Vance that the threat violated a reported memorandum of understanding reached days earlier, which committed the sides not to threaten or attack each other during the negotiation period.

“Today your president has issued threats. Understand that we never negotiate under threats or pressure,” Ghalibaf said. He then ended the direct face-to-face meeting. “The American side sought another meeting through the mediators, but we refused,” he added.

The episode showed how Trump’s public pressure tactics became part of the negotiations themselves. Reports said Iran had studied Trump’s 1987 book, co-written with Tony Schwartz, and consulted psychologists in an effort to separate actual U.S. policy from Trump’s threats, sudden posts and negotiating theatrics.

The direct meeting broke down, but the process did not collapse. Talks continued through Qatari and Pakistani mediators, while Vance later said the sides had made progress. “We haven’t built the house, but we’ve laid a successful foundation,” he said.