US cannot stop NK without military force and NK is not going to back down because of US threats and yippiddy yap as NK military taunts and torture of US citizens prove.
Only now when NK claims they can deliver an international nuclear package is the US saying they will do something about stopping NK. Well, how about stopping them before they got to this stage? They couldn't, otherwise they would have. And now, they can't stop them either without military force. The US invaded Iraq, killed SH and his family overthrowing that government -which stands as a warning against weak dictators that won't play ball with US. How weak is NK?
If NK already has nukes, it is too late to stop them. Amidst all the internal US problems, war with NK at this time could cripple the US more.
What is likely to happen is a diplomatic settlement wherein the US will have to play ball with NK same as the world has to do with China, Russia and Pakistan - try stopping them from having nukes.