When Donald Trump is allowed to speak without the aid of notes or a teleprompter, he has a tendency to say alarming things. There is, of course, his uncontrollable compulsion to promote his business interests at every turn, like when he told Maria Bartiromo about the “beautiful piece of chocolate cake” he was eating at Mar-a-Lago while U.S. destroyers were raining missiles down on Syria. There are his outrageous and easily debunked claims, such as his off-the-cuff remark about how he invented the phrase “priming the pump.” There are the wildly cringe-worthy moments, like when he implied Frederick Douglass was still alive or asked a black reporter to set up a meeting with the Congressional Black Caucus, assuming that they must be friends. But above all else, the one thing that consistently sticks out as cause for concern are Trump’s crimes against the English language.

The majority of Trump sentences are sentence fragments. Words are arranged in a way that only he can understand (“There is no collusion between certainly myself and my campaign, but I can always speak for myself, and the Russians, zero”). His limited vocabulary has the sophistication of a 7-year-old, which might explain why, when commenting on the bombing of an Ariana Grande concert in Manchester earlier this week, he described the perpetrators as “evil losers.” As mere arm-chair psychologists and speakers of the English language, many have concluded, based on his oratory style, that something is wrong with the president. MSNBC’s Joe Scarborough has described the president as “a man in decline,” Andrew Sullivan has mused that he is “incapable of accepting reality” and “bonkers,” and Keith Olbermann has suggested, more bluntly, that Trump has a “mental illness.”

But what do actual psychologists think? Are things actually as bad as they seem, neurologically speaking? Health Web site STAT analyzed decades of Trump’s on-air interviews and spoke with psychologists, psychiatrists, and experts in cognitive assessment and neurolinguistics who've observed the ex-reality TV show host, and concluded that, at the very least, “there had been a deterioration” in Trump’s brain.