In dealing with North Korea's provocative acts the Bush Administration is essentially limited to threatening "further isolation" for the North Korean regime. Forgive me for my denseness, but for a couple of reasons I don't see how that is a strategy that has any chance of success.
First, given the ongoing isolation of the North Korean government, there isn't a lot of room to "further isolate" them. I don't believe they have much engagement with the outside world save the six party talks, which haven't been convened for a meeting in over one Friedman. So what can we take away in order to make things harder on them?
Furthermore, the Chinese give tremendous amounts of food and energy aid to the North Koreans, and those shipments are not going to cease. It seems the Chinese have made the choice that stability in their adjacent neighbor's countries is more important than halting the advancement the of North Korean nuclear program - this despite the fact that the Japanese, with a constitutional amendment and a few scant months, could start their own nuclear weapons program spawning yet another regional arms race. Without aggressive leadership by the Chinese threatening their aid shipments and thereby the day-to-day lives of much of North Korea's population, neither the six party talks nor potential bilateral talks have much in the way of real leverage.
Finally, the reason we say "isolation" is something to be avoided for the North Koreans is that international engagement would facilitate improvements in North Korea's economy, and therefore improve the standard of living for its people. But we've seen time and again that the government does not care about the wellbeing of its people on the individual scale. In fact, the poor conditions in the country are an express benefit for the government, since it allows the largesse of the Party to be preferentially delivered to supporters. Localized starvation conditions are a boon, because P'yongyang can use those conditions to solidify support and weaken opposition. The government's advantage gained by the poor quality of life in the country is a further reason that our leverage is so weak without China's commitment. In order to have the desired impact on the government, the sanctions would have to be broad and almost unduly harsh - visiting those hardships directly on the citizens of North Korea, and hopefully thereby pressing them to defy their government in order to continue their own survival.
So, threatening isolation is not a real plan. I doubt people in the Bush Administration have any faith in it as a strategy, but what else do they have? They have to go on TV and say something.