Trump first voiced the unsound claim that vaccines cause autism during a 2007 interview with the Orlando Sun-Sentinal. Trump said his then-infant son Barron was being given vaccinations over a prolonged period of time, explaining, “When I was growing up, autism wasn’t really a factor. And now all of a sudden, it’s an epidemic. Everybody has their theory. My theory, and I study it because I have young children, my theory is the shots.”

In a 2009 Fox News segment, Trump called to say, “I think the vaccines can be very dangerous. And, obviously, you know, a lot of people are talking about vaccines with children with respect to autism.” He reiterated the claim again in a 2012 interview with Fox News on Autism Awareness Day.

Trump has also voiced this belief via Twitter.

During the 2015 Republican Presidential Primaries, Trump said he was supportive of vaccines, but again stated his belief that the dosages should be smaller and administered over a longer period of time.

Orlando Sun-Sentinal – Trump: Autism Linked to Child Vaccinations
Insider – The powerful media mogul at the core of Trump’s debunked views on vaccines and autism
The New York Times – President Trump on Vaccines: From Skeptic to Cheerleader