Preeptive War in America - Dead or Alive?

If Barack Obama is the next president, many among us will be assuming that the doctrine of preemptive war (that American can start a war with a terrorist state without being first attacked) is dead. But politicians have a way of adopting any policy - even that of their rivals - if it means getting done what they want done.

I am interested in what Mod-Bloggers think about preemption and whether it remains a viable political philosophy for the future? Has the Iraq War disproven it? Has it proven its effectiveness? Or was it all smoke and mirrors, anyway?

My own opinion was that it was always a bad idea, based on principles that we used to consider un-American. It was a knee-jerk reaction to 9/11 which cooler heads would have rejected in time, if it had not been used immediately to justify the invasion of Iraq. I think the next president would do well to abandon it. But I suspect they will only do so, if Congress works to regain their Constitutional power over declaring and funding wars.