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But despite ratcheting up the tension, Trump doesn’t really have a nuclear 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.

Photo by Drew Angerer/Getty Images

Earlier Tuesday, Trump sounded open to the possibility of an inter-Korean dialogue after Kim made a rare overture toward South Korea in a New Year’s address. But Trump’s ambassador to the United Nations insisted talks would not be meaningful unless the North was getting rid of its nuclear weapons.

In a morning tweet, Trump said the U.S.-led campaign of sanctions and other pressure were beginning to have a “big impact” on North Korea. He referred to the recent, dramatic escape of at least two North Korean soldiers across the heavily militarized border into South Korea. He also alluded to Kim’s comments Monday that he was willing to send a delegation to the Winter Olympics, which will be hosted by South Korea next month.