President Donald Trump said the next U.S. president should be physically and mentally capable of dealing with "sharp" world leaders, including Turkish President Recep Tayyip Erdoğan, Chinese President Xi Jinping and Russian President Vladimir Putin.

Talking about the details of a cognitive test he recently passed, Trump said he has the "mental stamina" to be U.S. president.

"Because I can tell you President Xi (Jinping of China) is sharp, (Russian) President (Vladimir) Putin is sharp, (Turkish President Recep) Erdogan is sharp. You don't have any non-sharp people that you're dealing with," Trump told Fox News.

The U.S. president revealed a part of the cognitive test he took, although he did not go into much detail about its content.

"Like a memory question. It's like, you'll go: Person. Woman. Man. Camera. TV," the president said. "So they say, 'Could you repeat that?' So I said, 'Yeah. It's: Person. Woman. Man. Camera. TV.'"

"Then, ten minutes, 15, 20 minutes later they say, 'Remember that first question... Give us that again."

"And you go: 'Person. Woman. Man. Camera. TV.'"

"And they say 'that's amazing. How did you do that?'"

"I do it because I have, like, a good memory," Trump said, adding that he is "cognitively there."

The U.S. president also urged his Democratic rival, Joe Biden, to take a similar test to prove that he is mentally stable because "something's going on."

"In a way, he has an obligation to," Trump added.