Sitting on a panel at the World Economic Forum in Davos, Switzerland Tuesday, Kerry first struggled for words when asked what he would say to the president if he were sitting opposite him.

“I can’t play that—I just…” he began. “He doesn’t take any of this seriously. He doesn’t have an ability to have that kind of conversation.”

“What would you say to him to get it serious?” the panel moderator asked.

“Resign,” said Kerry, this time not missing a beat. The audience reacted with applause.

Kerry has long been critical of the president, once comparing Trump’s claim to renegotiate the Paris Agreement to O.J. Simpson’s promise to find the person he says murdered his wife. At other points throughout the Trump administration, Kerry has called the president “delusional” and said that he is “steadily destroying our reputation in the world.”

Kerry is one of many world leaders, executives, and academics who converged in Davos this week for the annual World Economic Forum, where they will discuss global co-operation, the tech revolution, and climate change.

Trump initially planned to be in Davos for the economic forum but canceled his travel plans due to the partial government shutdown, which has now stretched into a month.

If Trump were to heed Kerry’s advise (an unlikely scenario), he would become only the second president to resign in U.S. history—the first being Richard Nixon, who stepped down in 1974 after it was realized he attempted to cover up his associates’ illegal activities in the Watergate scandal.