President Barack Obama criticized Republican frontrunner Donald Trump as unfit for the presidency during a press conference held on Tuesday.

Speaking in California after a meeting of leaders from Southeast Asia, Obama spoke about the difficulty of being president and reiterated his belief that Americans would not elect Trump.

"I continue to believe that Mr. Trump will not be president. I have a lot of faith in the American people. And I think they recognize that being president is a serious job," Obama said. "It's not hosting a talk show or a reality show. It's not promotion. It's not marketing. It's hard."

The president's remarks also touched on the new Supreme Court vacancy, the Islamic State, and the Democratic primary campaign. Obama said he would move to fill the seat opened up by the death of Justice Antonin Scalia over the weekend.

After saying he doesn't believe Trump will be elected, Obama detailed the magnitude of the challenges that face the president.

"Whoever's standing where I'm standing right 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 — and is often responsible for not just the United States of America, but 20 other countries that are having big problems," Obama said.

Here are the president's comments on Trump: