Has the United States ever elected a Muslim as its president?

History books will say no, but for Republican presidential candidate Donald Trump this has already happened when Americans picked Barack Obama as their leader.

In an interview with Chuck Todd on NBC's "Meet the Press" on Sunday morning, the controversial business tycoon once again cast doubts on Obama's faith.

When asked by Todd how he would react if a Muslim becomes US President, Trump replied, "Would I be comfortable? I don't know if we have to address it right now. But I think it is certainly something that could happen."

The Republican presidential aspirant went on and said, "I mean, some people have said it already happened, frankly. But of course you wouldn't agree with that."

Trump was presumably referring to Obama, whose faith and nationality he has repeatedly questioned even before joining the presidential race.

In 2011, Trump called on the White House to release Obama's birth certificate to prove that the US President is indeed an American. When the document was released showing that Obama was born in Hawaii, Trump questioned its authenticity.

Pressed further by Todd during the interview if he believes Obama is a Christian, Trump said he did not "talk about people's faith" and that he was "willing to take [the president] at his word."

Despite his doubts on Obama's faith, Trump said over the weekend that he "love[s] the Muslims" and thinks "they're great people." The Republican presidential candidate, however, pointed out that there is still a "severe problem" concerning Muslims.

"I feel strongly that Muslims are excellent. I know so many Muslims that are such fabulous people. But there is a problem. I mean, there's no question about it," Trump said.

"We can be politically correct and we can say there is no problem whatsoever. But the fact is there is a problem with some. And it's a very severe problem," he added.

The issue of candidates and their faith came into the forefront last week after one of Trump's supporters also insinuated during a campaign event that Obama was a Muslim, and that Muslims "have training camps growing where they want to kill us."

Trump drew flak for not correcting the unidentified man's statements, but the controversial businessman later on defended his inaction by saying he is not obliged to defend Obama.