Two years after President Obama released his birth certificate, Trump said it was not believable to some people. "You know, some people say that was not his birth certificate," he told ABC in August 2013. "I'm saying I don't know. Nobody knows and you don't know either."

Trump posted multiple tweets in 2012 citing an anonymous source, as the Daily Beast's Colin Jones noted.

Trump said one of the sources "called my office." 

Trump took care to describe this source as "extremely credible." 

Trump so often sources information to "many people" (without naming any of them) that there's a well-worn #manypeoplearesaying hashtag on Twitter. The Washington Post wrote an article about it, which includes the examples on the next three slides.

At a rally in September, a man in Trump's audience said President Obama was a Muslim and “not even an American,” then asked Trump to get rid of Muslim “training camps.”

“You know, a lot of people are saying that, and a lot of people are saying that bad things are happening out there,” Trump responded. 

In early January, Trump said he had heard from many Republicans worried that his rival, Sen. Ted Cruz, was born in Canada.

“I’d hate to see something like that get in his way, but a lot of people are talking about it, and I know that even some states are looking at it very strongly, the fact that he was born in Canada and he has had a double passport,” Trump told the Post.

In May 2016, Trump told the Post what some "people" believe about the death of Vince Foster. “I don’t bring [Foster’s death] up because I don’t know enough to really discuss it,” Trump said. “I will say there are people who continue to bring it up because they think it was absolutely a murder. I don’t do that because I don’t think it’s fair.”

Soon after Trump called for an end to anonymous sourcing, The Associated Press noted, "Members of Trump's White House team regularly demand anonymity when talking to reporters."