Two days after Donald Trump said that President Obama had founded the Islamic State, and a day after he insisted that he meant what he said, the Republican presidential nominee reversed himself on Friday and claimed the statement was nothing more than sarcasm.

It’s the latest instance of an emerging pattern with Trump: an inflammatory statement, an ensuing political controversy, silence from his campaign, then backtracking. A candidate who soared to the top of a field of 17 Republican primary contenders in part by provocative declarations finds himself adjusting to a general election in which even some officials in his own party have raised concerns about his temperament.

“This is unique in the annals of presidential campaigns, at least in the last 30 or 40 years,” said Martin Medhurst, a communications professor at Baylor University who studies presidential rhetoric. “You can use that once or twice and get away with it, but you can’t use it over and over again because very quickly people say it’s not sarcasm: It’s covering your you-know-what.”

In a campaign, Trump’s self-contradictions and corrections provide talking points to his opponent. But loose rhetoric could be “catastrophic” coming from a president, Medhurst said.

“Every word that comes out of a president’s mouth is examined. It is parsed for the slightest change in meaning or motivation,” Medhurst said. “A president who conducted himself the way Mr. Trump is conducting himself would throw our diplomacy and our foreign policy into absolute chaos.”

In a rally on Wednesday, Trump repeatedly said that Obama was the “founder” of Islamic State. When conservative radio host Hugh Hewitt suggested in an interview with Trump the next day that perhaps he meant Obama’s policies had allowed the group to flourish, Trump responded, “No, I meant he’s the founder of ISIS. I do,” using an acronym for the group.

Obama, of course, did not found Islamic State.

Trump criticized media organizations including CNN for their reporting on his remarks in a Tweet on Friday.

“@CNN reports so seriously that I call President Obama (and Clinton) ‘the founder’ of ISIS, & MVP,” Trump wrote, alluding to another comment he made that the president and Hillary Clinton, his Democratic rival in the 2016 election, were the terrorist group’s most valuable players. “THEY DON’T GET SARCASM?”

He has issued similar after-the-fact clarifications following other recent inflammatory statements. At a news conference July 27, he said “I hope” Russian intelligence services would hack Clinton’s emails. After a storm of criticism, he said a day later that the remark was sarcastic.

Earlier this week, Trump said at a rally that should Clinton be elected, only the “Second Amendment people” could prevent her from appointing Supreme Court justices hostile to gun rights. The remark was widely interpreted as an allusion to the possibility Clinton might be assassinated. The next day, Trump insisted he was simply exhorting gun-rights supporters to vote in the election, even though he had described a post-election scenario in which Clinton is already president.

Julian Zelizer, a presidential historian at Princeton University, said that claiming the sitting president is the founder of a terrorist organization “crosses a line” in campaign rhetoric.

That is especially so against the backdrop of Trump’s repeated accusations that Obama and Clinton have been soft on terrorism, his allegations of an “almost criminal” conspiracy that allowed Americans to die at the U.S. consulate in Benghazi, Libya, and the “lock her up” chants heard about Clinton at many Trump rallies, Zelizer said.

“In that context, it’s hard to just say, ‘well, this was simply a sarcastic remark that should be forgiven,’ ” Zelizer said.

The explanation belies the power of words uttered by candidates with committed followers, he said.

“What concerns me is that followers, supporters listen, and they can take a statement like that and do something dangerous with that,” Zelizer said. “They might either not hear his follow-up or they might not believe that he means what he says when he says he’s being sarcastic.”