"We're not going to allow North Korea to become a nuclear power."
Bull****. They are now, and the sooner we get our heads wrapped around that the better. We can take a shot at decapitating the regime, or we can attempt to disable their nuclear manufacturing, missile launching and warhead storage, but there is absolutely zero assurance that we'd be successful at getting it all. NK has know that was possible for years and has built hardened facilities and played shell games with camouflage. We can hit out best bets - but I remember how we were going to take out Saddam Hussein at the start of the Gulf War. If any are left after we have made that kind of strike, they'll be trying very hard to find a way to strike back, and we cannot afford any mistakes or oversight if they do. And sometimes, **** happens.
We're better off to realize that they have them but don't really want to use them any more than anyone else who has them does. They are a small country, and if they shoot first they can be functionally annihilated very quickly. They know the balance of power better than we do - but they also understand the balance of terror.
Ask people in Hawaii if they think we should take a crack at NK and see what answers you get.