[jyl]

This administration's foreign policy is fairly conventional. Who escalated the Afghanistan war?

The US has 30K troops in SK and pre-positioned equipment for many more. They will be among the first casualties. And the mutual defense commitment in SK is almost as old as NATO, breach that and there goes your military influence globally. No president other than a radical isolationist would fail to respond, and Obama is not that.

I actually think a war in Korea would escalate to nuclear when NK starts losing. Once NK fires the first nuclear missile, even if just a medium range one aimed at a purely military target in SK (how likely is that?) the game theory says that the US has to strike NK with nuclear weapons, massively (no eye for an eye stuff). Neither China nor Russia would get involved.