The problem with ICBMs is the level of technology required. For NK to be able to launch a missile with a nuclear warhead all the way to anywhere in the US will likely take a lot of time, if they can accomplish it at all. I mean, they can reach Japan, but that's a long way from the US. I'm not inclined to think that we'd spend all this money on missile defense just to send it to Japan to protect them. As for smuggling one in, this is ridiculously easy. Just send a ship into a port city, like New Orleans or New York, and blow it up while still on the ship. There's no reason to even chance it across port security. Since it's a nuclear explosion, it hardly has to be exploded at downtown for devastating effects.
a) The NK government is more than willing to starve millions of their people to free the resources to develop weapons. They have already surprised the world with their missile technology. Japan is one of our most critical allies, one of our biggest trading partners, if not the biggest, and a place where we have tens of thousands of our military. An attack on Japan from NK with a nuclear-tipped missile is an absolute disaster, not only for Japan, but for us. If they are able to threaten to do that, in a credible way, it is a disaster. b) See Hayes' post above. He makes good points, and I hope he is right, and we are lucky. Keep D&D Civil!!
Remember, meh, there are plenty of scientists from the former Soviet Union who need to feed their families now that the Soviet military has largely dissolved. I'm sure there are some in scenic North Korea now and let me tell you, Soviet rocket motor technology is the best in the world, even better than ours. As for their technology, Deckard is correct. They've surprised many with the range of their missiles. That is why we need TACTICAL missile defense that is able to move where we need it (I agree with everyone else, a fixed system is a boondoogle).
I think Japan is somewhere in the 3-5 range. I am almost positive that Canada and Mexico are the top 2.
even worse......how many realize how far inland the Houston Ship Channel goes? the end of the channel is less than 10 miles from downtown Houston. the scenario could go like this.....ship brings it in...bad guy stashes the device on one of the little motor launches that all ships have...and then lanches it and goes upchannel and detonates before any port authorities can get to them. I admit...not likely....but possible.
I'm quite familiar with the capabilities of N. Korean missiles. That still doesn't change the fact that there are easier ways to nuke an American city. ICBMs should be feared in the hands of military powers like the former USSR, or perhaps China in the future. Large scale missile attacks can be especially devastating and should be feared. Especially if they can cripple our ability to counterattack. But if a country(or terrorist organization) wants to just take one shot at an American city with a nuclear bomb, there's literally no reason to use a missile. It would be like taking a car to see your next door neighbor. Sure, you could do it, but it's much easier to just walk over.