Trump has long been one of the most vocal skeptics about Obama's birthplace and faith.
Four years ago, Trump mounted a campaign to pressure Obama to release his long-form birth certificate, even saying he would send investigators to Hawaii to find out the truth. The effort helped fuel the so-called "birther" conspiracy theory that held that Obama was born in Kenya -- and Trump also floated the idea that Obama's birth documents may label him a Muslim.
"He doesn't have a birth certificate. He may have one, but there's something on that, maybe religion, maybe it says he is a Muslim," Trump told Fox News in 2011. "I don't know. Maybe he doesn't want that."
His accusations reached such a high decibel level that in April 2011, Obama appeared in the White House briefing room to denounce Trump and release the long-form version of his birth certificate.
"We do not have time for this kind of silliness," Obama told reporters. "We've got better stuff to do. I've got better stuff to do."
Obama's staff posted the birth certificate on the wall of the White House briefing room to serve as a permanent answer to reporters who had additional questions. The certificate is accessible on the White House website.
On occasion, the President has turned the tables by lampooning Trump for his statements. During the White House Correspondents' Association dinner in 2011, Obama announced that he would release his official birth video — and then showed the opening scene from "The Lion King," to roars of laughter from the audience.
Trump, captured on camera during the dinner, looked unamused -- and refused to relent.
In 2012, after Madonna made what she later called an "ironic" remark on stage that Obama was "a black Muslim," Trump tweeted, "Does Madonna know something we all don't about Barack? At a concert she said 'we have a black Muslim in the White House.'"
And during a candidate forum in Iowa earlier this year, when asked about Obama's commitment to the United States, Trump replied, "I don't know if he loves America."
Questions about whether Trump intentionally encourages his supporters to believe such claims resurfaced at a campaign rally Thursday. Trump is under fire after he didn't correct a supporter who said Obama was not an American and was a Muslim.
"We have a problem in this country. It's called Muslims," a man attending Trump's rally in Rochester, New Hampshire, said. "You know our current president is one. You know he's not even an American.""We need this question," Trump said, chuckling. "This is the first question."
The man continued: "We have training camps growing where they want to kill us. That's my question: When can we get rid of them?"
"We're going to be looking at a lot of different things," Trump said. "You know, a lot of people are saying that and a lot of people are saying that bad things are happening. We're going to be looking at that and many other things."
After the event, Trump's campaign manager told CNN that the GOP front-runner didn't hear the first part of the man's statement.
"All he heard was a question about training camps, which he said we have to look into," Corey Lewandowski said. "The media want to make this an issue about Obama, but it's about him waging a war on Christianity."
The White House slammed Trump on Friday.
"Is anyone really surprised that this happened at a Donald Trump rally?" White House spokesman Josh Earnest said during his daily briefing. "The people who hold these offensive views are part of Mr. Trump's base. ... It is too bad that he wasn't able to summon the same kind of patriotism that we saw from Senator McCain, who responded much more effectively and directly when one of his supporters and one of his campaign events seven years ago raised the same kind of false claims."
The man who asked the question, in fact, represents a majority of Trump's supporters who also believe Obama is secretly harboring faith in Islam, according to a CNN/ORC poll
conducted earlier this month. That poll found that 54% of Trump supporters believe Obama is a Muslim. Among Republicans nationwide, the poll showed, 43% of Republicans think Obama is Muslim, as do 29% of Americans as a whole.
Trump isn't the only Republican presidential candidate to question Obama's faith: In February, Wisconsin Gov. Scott Walker told the Washington Post
that he was unsure of the president's commitment to Christianity.
"I've actually never talked about it or I haven't read about that. I've never asked him that," Walker said. "You've asked me to make statements about people that I haven't had a conversation with about that. How (could) I say if I know either of you are a Christian?"
Questions about Obama's commitment to the country and faith have long dogged presidential candidates.
In 2012, Rick Santorum, a presidential candidate then and now, also ignored a statement from a campaign supporter
accusing Obama of being an illegitimate president and "an avowed Muslim."
"I never refer to Obama as President Obama because legally he is not," a woman told Santorum during a campaign event in Florida. "He constantly says that our constitution is passé, and he ignores it as you know and does what he darn well pleases. He is an avowed Muslim and my question is, why isn't something being done to get him out of government? He has no legal right to be calling himself president."
Santorum later said it wasn't his responsibility to correct the record every time a supporter makes an incorrect statement.
"I don't feel it's my obligation every time someone says something I don't agree with to contradict them, and the President's a big boy, he can defend himself and his record and I'm going to go out and talk about the issues that the President and I disagree on and try to defeat him because I think that's the best thing that we can do for the future of our country," he told CNN at the time. "My position is clear, the President's position is clear. I don't think the President's a Muslim, but I don't think it's my obligation to go out and repeat that every time someone who feels that way says something."
In a now-famous exchange during a townhall in 2008, Republican presidential nominee John McCain took the microphone away from and corrected a woman who called Obama "an Arab."
"No ma'am," McCain said. "He's a decent family man citizen that I just happen to have disagreements with on fundamental issues."
And in 2008, Hillary Clinton was criticized for saying Obama wasn't a Muslim "as far as I know." On Friday, she condemned Trump's latest remarks and said she was "appalled."
"Not only was it out of bounds, it was untrue," she said. "He should have from the beginning corrected that kind of rhetoric, that level of hatefulness."