Just sifting through TW's post, I think there are two points. He's my take on these ideas - as far as I can make them out.
One is military. Sure, the US would win a conventional war Vs North Korea (provided China stayed out of it) - but, then what?
How long until the liberators would be viewed as occupiers? Would there be a guerrilla campaign? and the real biggie ... how could the US rebuild a stable nation ready for reintegration into the local neighbourhood, out of people who have been brainwashed for 50 years that the rest of the world, especially the USA and South Korea, are pure evil and want to destroy them?
Which leads to the second point, which is political. UG is right that the US military would make short work of the conventional PDRK military, but this is only part of the question. Without a workable political solution, military victory is in the long term futile. This was the problem in Vietnam and has been the problem in Iraq and Afghanistan.
"If all you have is a hammer, you tend to see every problem as a nail." The US has one hell of a hammer, but if the job is changing a light bulb, the hammer just makes it harder.
So the deja vu TW is on about is that this
military ability gets the US into
political quagmires. Sure, the conventional war would be won... then what? Nation building is not the US's forte. Imagine trying to do it out of the screwed up mess that a post-war North Korea would be.
Oh and don't forget ... they DO have The Bomb. If they were cornered, as a last resort, using a tactical battlefield strike within their own territory ... I wouldn't rule it out.
I'm probably wrong in my TW scholarship. My apologies to you TW if I've got you way wrong. But TW? "Deja vu". Not "vue". Or "déjà vu" to be really precise.
