Trump's plan to destroy North Korea

Exactly what does Trump mean when he says he can destroy North Korea? Perhaps Jim Mattis, his trusty defence secretary, has come up with a plan to literally obliterate North Korea from the face of the earth. Is this possible? Is this just Trumpism or is there really a military option which can do this? Well, of course there is. It's the nuclear option. Dropping 500 tactical nuclear bombs on every military/nuclear site and Kim Jong-un's residence, destroying in a wave of B52, B2 abd F35 nuclear attacks North Korea's ability to retaliate. Hiroshima and Nagasaki on a huge scale. Total annihilitation. But even if North Korea had launched a preemptive nuclear strike on, say, Los Angeles, would the president of the United States have carte blanche to eliminate a whole country and reduce its people to a smouldering radioactive graveyard? Is this truly what Trump has in mind when he talks of destroying North Korea? I cannot envisage any other way of annihilating a country. Massive bombing with ccnventional munitions would never have such a result. It would be devastating but North Korea would survive, and would still be able to retaliate. Trump sometimes speaks off the cuff and does so with rhetorical hyperbole, and the world has got used to that. But this was a speech to the United Nations General Assembly. The speech was written down. It clearly included the words, "I will totally destroy North Korea." So there must be a nuclear option on the list of potental military action put together by Mattis. If I'm thinking this, then so must Kim Jong-un. Hopefully, that is what Trump had in mind, to scare Kim. But trying to scare Kim doesn't seem to work. So I'm guessing Trump must have asked Mattis one big question when the retired four-star Marine Corps general presented him with the military options for attacking North Korea: "Can I launch a nuclear attack on North Korea if Kim sends a nuclear ballistic missile to hit the United States?" The only answer I guess is: "Yes, Mr President."