A North Korean attack, although ultimately doomed to failure, could also be very costly in terms of South Korean and US lives. If the North has usable nukes, they don't need missiles to deliver them to be militarily effective. Nukes delivered by fishing boats or mini-subs to the harbors of South Korea and detonated would make it impossible to land reinforcements. Short range missile strikes or artillery with chemical-biological warheads could render air bases unusable, thus complicating a US response. We have the air power and naval power to respond, but there will be a bloody first quarter in this war. In the end, we prevail...if we have the determination and will. Our capacity to endure casualties is part of their thinking.