WASHINGTON (AP) — The Latest on President Donald Trump and North Korea (all times local):

3:50 p.m.

The White House is defending President Donald Trump's Twitter riposte to North Korean leader Kim Jong Un's boast about his "nuclear button."

Press Secretary Sarah Huckabee Sanders says, "I don't think that it's taunting to stand up for the people of this country," adding that people should be concerned about Kim's "mental fitness."

Her statement comes after Trump took to Twitter Tuesday to respond to Kim's claim that he possesses a nuclear button on his desk. Trump tweeted, "I too have a Nuclear Button, but it is a much bigger & more powerful one than his, and my Button works!"

Pressed on Trump's claim, Sanders says, "I think it's just a fact."

The president does not possess a physical button to launch nuclear weapons.

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3 a.m.

President Donald Trump boasted that he has a bigger and more powerful "nuclear button" than North Korean leader Kim Jong Un does — but the president doesn't actually have a physical button.

The process for launching a nuclear strike is secret and complex and involves the use of a nuclear "football," which is carried by a rotating group of military officers everywhere the president goes and is equipped with communication tools and a book with prepared war plans.

If the president were to order a strike, he would identify himself to military officials at the Pentagon with codes unique to him. Those codes are recorded on a card known as the "biscuit" that is carried by the president at all times. He would then transmit the launch order to the Pentagon and Strategic Command.