U.S. President Barack Obama believes that Donald Trump will not succeed in taking over the White House, saying he has confidence that the American people will not entrust America's nuclear launch codes to the billionaire reality TV show star.

"I continue to believe Mr. Trump will not be president, and the reason is because I have a lot of faith in the American people. And I think they recognise that being president is a serious job," Obama said at a news conference in California on Tuesday. "It's not hosting a talk show or a reality show. It's not promotion. It's not marketing. It's hard."

Obama conceded that Trump has attracted many supporters as shown by his recent victory in the New Hampshire primary and likely victories in some other early primary states, USA Today reported.

However, he predicted that Trump's popularity would fade away as the November general election gets nearer.

"Yeah, during primaries people vent [their frustration], and they express themselves, and it seems like entertainment, and oftentimes it's reported just like entertainment. But as you get closer, reality has a way of intruding," Obama said.

Obama has long been critical of Trump, particularly his expressed foreign policy and especially his anti-Muslim rhetoric. On Tuesday, the outgoing U.S. president sharpened his criticism of Trump's credentials, using his hosting of leaders from 10 Southeast Asian countries as an example.

The job of president, Obama said, requires working with world leaders in a way that "gives people confidence that you know the facts, and you know their names, and you know where they are on a map, and you know something about their history."

Obama appeared to be alluding to Trump's apparent lack of knowledge on foreign policy matters as shown by the Republican candidate's replies to some of the questions on the subject thrown his way.

"Whoever is standing where I'm standing now has the nuclear codes with them, and can order 21-year-olds into a firefight, and has to make sure that the banking system doesn't collapse," Obama said. "The American people are pretty sensible, and I think they'll make a sensible choice in the end."

Obama pointed out that Trump is not the only Republican presidential candidate with "troubling" foreign policy objectives.

"He [Trump] may up the ante in anti-Muslim sentiment, but if you look at what the other Republican candidates have said, that's pretty troubling, too. He may express strong anti-immigration sentiment, but you've heard that from the other candidates as well," Obama said.

He cited the case of Sen. Marco Rubio. "You've got a candidate who sponsored a bill, that I supported, to finally solve the immigration problem, and he's running away from it as fast as he can," Obama said.

On the two Democratic candidates, Obama said there is little difference between Sen. Bernie Sanders and his former Secretary of State, Hillary Clinton. He said they agree more than they disagree, and that their campaign messages were largely about tactics.

"They believe in climate change. They think science matters. They think that it's important for us to have some basic regulations, to keep our air clean and our water clean, and to make sure that banks aren't engaging in excesses that can result in the kind of thing that we saw in 2007 and 2008. So there's a broad convergence of interests around those issues," he said.