Trump's 10 favourite conspiracy theories

As Donald Trump at the weekend withdrew his allegation that President Barack Obama was not born in the United States, he offered another debunked accusation in its place: that his Democratic rival, Hillary Clinton, created the "birther" movement before he became its champion.

That moment marked the latest instance in which the Republican presidential nominee has elevated a discredited allegation - echoing comments circulating on social media - and injected it into the presidential contest.

Trump has regularly come under fire for repeating unfounded rumours as fact, and has been challenged by fact-checkers and opposition groups on scores of statements he has made.

Below is a short history of similar unsubstantiated claims Trump has repeated.

1 That Obama did not attend Columbia University

At the height of birther movement, Trump also insinuated on occasion that the President had not truly attended Columbia University. Trump once also offered US$5 million to charity if Obama released his college transcripts, which he hoped would reveal the President's birthplace.

"Our current president came out of nowhere. Came out of nowhere," Trump said in 2011 at the annual Conservative Political Action Conference, according to a transcript by PolitiFact.

"In fact, I'll go a step further: The people that went to school with him, they never saw him, they don't know who he is. It's crazy."

2 That Trump's taxes were the subject of an audit because he's a Christian

In another instance in February, Trump said that his tax returns may be under audit by the Internal Revenue Service because of his religious faith.

"Well, maybe because of the fact that I'm a strong Christian, and I feel strongly about it and maybe there's a bias," he said during a CNN interview.

"I can tell you one thing: I am audited when I shouldn't be audited," Trump said later. "I tell my people: Why is it that every single year, I'm audited, whereas other people that are very rich, people are never audited - and they don't even know what I'm talking about when I talk about audits."

3 There's something "very fishy" about Vince Foster's death

Trump's claims have echoed theories and conspiracies popping on social media and various fringe blogs on the Internet.

In May, Trump suggested that something was amiss in the "very fishy" suicide of former White House aide Vince Foster, which has been at the centre of conspiracy theories for decades.

"He had intimate knowledge of what was going on," Trump told the Washington Post in May, speaking about Foster's connection to the Clintons. "He knew everything that was going on, and then all of a sudden he committed suicide."

4 That Antonin Scalia may have been a victim of foul play

When Supreme Court Justice Antonin Scalia's death was announced in February, Trump spread rumours about potential foul play:

"And it's a horrible topic. But they say they found a pillow on his face, which is a pretty unusual place to find a pillow. I can't tell you what - I can't give you an answer. You know, usually I like to give you answers," Trump told a conservative radio host, Michael Savage. "But I literally just heard it a little while ago. It's just starting to come out now."

5 That Ted Cruz's father, Rafael, was linked with JFK's assassin

In May, citing a National Inquirer cover, Trump suggested that the father of GOP primaries rival Senator Ted Cruz had been involved with President John F. Kennedy's assassin, Lee Harvey Oswald. That connection was uncorroborated, and Cruz, blasting Trump, called the real estate developer a "pathological liar".

Trump threatened his own efforts to unify the party in July - the day after he formally accepted the GOP nomination - when he repeated the claim at a news conference where he tore into Cruz because the senator refused to endorse him during a prime-time speech.

6 That vaccines are connected to autism

Last year, Trump stirred controversy during a presidential debate when he said that vaccines may cause childhood autism.

"The child, the 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 said. "I'm in favour of vaccines. Do them over a longer period of time. Same amount, just in little sections."

7 That he witnessed thousands of Muslims celebrate 9/11 in New Jersey

Trump claimed last year that he had witnessed on television thousands of Muslims celebrating the collapse of the World Trade Centre on September 11, 2001. No such footage has ever materialised.

"There were people that were cheering on the other side of New Jersey, where you have large Arab populations. They were cheering as the World Trade Centre came down," Trump said on ABC News in November, one day after he made similar claims at a campaign event.

"I know it might be not politically correct for you to talk about it, but there were people cheering as that building came down - as those buildings came down. And that tells you something. It was well covered at the time, George."

8. That he was attacked by Isis (Islamic State)

After a man charged security barricades in March during a campaign event in Dayton, Ohio, Trump insisted that the young man was a member of Isis because of a hoax Internet video he and his staff had seen circulating online.

The man, who had attempted to rush the stage, was charged with disorderly conduct but no ties to Isis were found. Pressed on that later during an interview with Chuck Todd on NBC, Trump insisted: ""No, no, no, no. He was, if you look on the Internet, if you look at clip," Trump said.

9 That climate change is a hoax

Trump received flak for suggesting years ago that climate change is a hoax created by the Chinese. Earlier this year he walked back that statement and said that he was joking.

The concept of global warming was created by and for the Chinese in order to make US manufacturing non-competitive.

10 That Obama bribed New York's attorney-general to investigate Trump University

At times, Trump's claims have seemed calculated to deflect attention away from himself. At a campaign rally in February, Trump insinuated that Obama had bribed New York Attorney-General Eric Schneiderman to launch the investigation against Trump University, the embattled for-profit education business licensing Trump's brand.

"The attorney-general of New York meets with Barack Obama in Syracuse," Trump said, according to a transcript by the Huffington Post. "The following day he sues me. What they don't say is, I believe, US$15,000 or a lot of money was paid to the attorney-general by the law firm in California that is suing me."