While the US invaded a country--led by an undoubtedly evil dictator--on the pretense of destroying weapons of mass destruction that apparently no one with access to undoctored intelligence thought Iraq had, North Korea has gotten so far ahead with its own widely-publicized and acknowledged program that they are, even now as I type this, fueling an ICBM capable of reaching the United States.
Other than the presence of oil in one of these countries, the grudge that we held against Iraq both for the invasion of Kuwait and Saddam's funding of an attempt on the earlier President Bush, the hard-on neo-cons have had for Iraq for the last twenty years and the non-existent connection between secular Baathism and world-imamate al-Qaeda, what are the relevant policy differences that have led us to essentially ignore this threat (or, rather, to treat it diplomatically, where "diplomatically" means both refusing to talk to North Korea and not really bringing any significant pressure to bear)?
Unfortunately, I don't know what we can do about North Korea. Kim is insane, the government is willing to starve its people for military spending, the country is already a pariah, there is little that we can imagine that sanctions would achieve. But at the same time, it seems that our government has thrown a lot of money and resources (though not planning) at a country that was, at best, a distant threat, while ignoring a very real and immediate danger, a North Korea with ballistic missiles.
So, if you really think your most important job is protecting Americans, you aren't even living up to your own standards, President Bush.