IMHO: On North Korea (NK), Trump is building rings and layers of responses and forces, at first to defend the US, South Korea (SK), and Japan and then to get rid of Kim and his military equipment, missile program, and nuke program. So, Trump's rings and layers are first defensive and then offensive.

The urgent purpose of the defensive parts are to deter Kim from shooting at the US, SK, Japan, Guam, Australia, England, .... Here the message is clear: If Kim explodes a nuke, the US will respond so that Kim's first nuke will he his last one.

For the defensive parts, he has been pursuing UN sanctions and lining up other countries against NK. He has positioned off the coasts of NK a Nimitz class aircraft carrier, several smaller ships, an attack submarine (in case Kim does something hostile with a submarine), and an Ohio-class missile firing submarine (SSBN) (in case Kim explodes a nuke). Apparently the British are sending a ship with some Mach 3 missiles maybe able to destroy an ICBM during launch or boost phase. Trump has positioned USAF planes at least in Guam and maybe in other west Pacific bases and held joint exercises with SK. He has authorized SK and Japan to buy some more advanced US weapons and has authorized SK to have more throw weight on their missiles (somehow the US retains some legal rights, soon to end, over SK from the Korean War). SK has been deploying US THAAD anti-missile systems. The US has been testing its anti-ballistic (ABM) systems, the ones designed to intercept a warhead during reentry.

Trump had a White House meeting on NK with Mattis and Dunford and likely also Kelly, McMaster, and others and then had Mattis, with Dunford, make a strong statement that, to translate, if NK exploded a nuke then the US would make that first nuke the last one, and for this the US has several options, some nuclear, some non-nuclear.

So, maybe for such largely defensive steps Trump's goal is to keep Kim from exploding a nuke right away.

So, there are geographical rings from SK to Japan, Guam, and the US, e.g., short range defenses and long range defenses. And there are diplomatic layers from SK, China, Russia, the UN, the US, other countries, etc.

For offense, Trump claims he talked with Xi and got him to say that he agreed that NK should not have nukes.

It looks like Trump has decided that NK will not have missiles or nukes. If Kim wants to give up missiles and nukes peacefully, then maybe that will be enough. Otherwise Trump will work to have the missiles and nukes destroyed, to have Kim removed from office, say, moved out of the country and/or killed, and to have the NK military equipment, e.g., rockets, artillery, guns, trucks, submarines, other ships, etc. destroyed.

The US Navy Seals have been training with some SK soldiers on how to take out someone, likely Kim, like the Seals took out UBL. Broadly it begins to look like the US and SK have decided that SK will do most of the fighting.

So, maybe a fight would go: (A) The Seal trained SK soldiers cross into NK and kill and/or capture Kim. (B) Enough of the NK leadership and military command and control will be captured or destroyed to stop NK from shooting missiles, artillery. (C) SK will launch some hyper accurate missiles at the NK missiles ready to be launched. (D) The SK army, backed from the air by the USAF and Navy, will invade NK, take over the government and missile and nuke infrastructure and destroy that infrastructure. (E) China has troops on the NK border to keep NK civilians from entering China. Russia may do something similar. (F) The SK army will destroy essentially all the NK military equipment, e.g., artillery. (G) SK will turn NK over to the UN and leave.

All the important steps will be over in just a few minutes or hours. Step (G) will take no more than some weeks.

Then Kim and his military, missiles, and nukes will be gone. The NK leadership in missiles and nukes will be gone. The US will never set foot in NK. There will be very few civilian deaths. Little or no radiation will be released.

All that is just a guess.