In one of the stranger moments in CNN’s Wednesday-night Republican debate, moderator Jake Tapper pitted Donald Trump—who is most definitely not a doctor—against retired neurosurgeon Ben Carson on the subject of Vaccines: Do They Cause Autism or Not? The answer, as Carson explained, is absolutely not. But Trump had his right of reply:

“Autism has become an epidemic. Twenty-five years ago, 35 years ago, you look at the statistics, not even close. It has gotten totally out of control,” Trump said. “I am totally in favor of vaccines. But I want smaller doses over a longer period of time. Same exact amount, but you take this little beautiful baby, and you pump—I mean, it looks just like it’s meant for a horse, not for a child, and we’ve had so many instances, people that work for me.”

He added: “Just the other day, 2 years old, 2½ years old, a child, a beautiful child went to have the vaccine, and came back, and a week later got a tremendous fever, got very, very sick, now is autistic.” Trump did not elaborate on whose child he was talking about.

Autism rates are going up, it’s true, but experts have ruled out vaccines as the cause. One of the likely reasons is that diagnosis techniques are catching more cases.

Claiming that you’re not opposed to vaccines, just that you want them to be safer or on a different schedule, is a common deflection technique among anti-vaccination conspiracy theorists. As Trump demonstrated, it’s a way to position yourself as reasonable while still perpetuating the false belief that getting your jabs is going to destroy your brain. Meanwhile, there’s no evidence that vaccines are safer if they’re spaced out more—all that does is open a window to disease exposure and increase the risk that a child could miss a vaccine altogether.

Politically, the moment was a perfect summation of Donald Trump’s candidacy: his ability to pair off-the-charts self-confidence with complete ignorance about whatever subject he’s opining about. His fans swoon over his braggadacio and willingness to speak his mind. But when those talents are paired with an utter disregard for the facts, that kind of confidence is dangerous.

Read more of Slate’s coverage of the GOP primary.