We really didn't have any choice but to trust the Russians from the early 1960's onward. We came darn close to blowing each other up on a few occasions. We are lucky it didn't come to that.
Dr. Evil over there in NK is acting rationally, in his own perverse way. He's gambling, that's for sure, but this is time to do it. It is obvious that the NK's don't believe that we can handle two large scale high intensity ground wars at the same time and probably believe that we wouldn't hit them with a pre-emptive nuke strike. A conventional strike that takes out their nuke facilities is very possible, but that entails a high degree of risk because Seoul is vulnerable to a counter-strike and they don't even have to get across the DMZ to do that. Sure, we take them out, but at what price? They are betting that we will cave before putting SK at risk. That may be a risky bet, but Kim may figure he's next, after Saddam, so he has little to lose in the end?
Any way you cut it, we are in a difficult position.