I'm going to use one of my precious diary entries on this because I'd like to dispell a popular misconception around here. Kerry is not decimating the field simply or solely because he "won Iowa". The situation is a bit more complex, although there was certainly a domino effect involved.
To test this out, imagine that Edwards (who with a key newspaper endorsement and a backroom Kucinich deal) was surging and actually came out on top in Iowa. Would he be the favorite going into New Hampshire? No. He'd get a lot of great press, but he'd still have to claw his way up through 2 favorite sons in NH who both had formidable operations there. Edwards was very low on money before Iowa. He would have gotten a boost after Iowa, but I doubt it would have been enough to make up the difference and get past
both Kerry and Dean. Not only that, I'm starting to question whether even if Edwards had won IA and NH, if he could have turned around to dominate states like WA or MI or AZ. Certainly, he could be stopped in ME. Also, if Dean had finished a lot closer to Kerry in Iowa, and not screamed, he might have been able to claw his way past Kerry in NH. At that point, I think Dean would still be doing quite well and be best placed to win the nomination.
Kerry is running the table because he won Iowa and New Hampshire, and he won New Hampshire because he won Iowa. What I mean by that is that he and Dean (polls notwithstanding) had the same advantages in NH, both being from neighboring states. Therefore, which ever of the 2 who placed higher in IA would have the advantage going into NH, plus nobody could have anticipated the scream and the reaction. All Kerry had to do was win Iowa because he was well placed to roll that win into a win in NH. Same with Dean. Not the same with Edwards. Possible for Clark if he had competed in Iowa and won, since he'd worn the frontrunner mantle briefly after entering the race and was running second in national polls going into Iowa.
This again points to something that Kos mentioned early in the "how they can win" scenarios. Dean and Kerry are essentially running as the same candidate--from New England, strong competitor, good credentials, runs well in the "blue states". Despite what we see here with the sniping, the average voter could substitute one for the other without too much difficulty. Therefore only one could come out the victor. If Dean had internalized this, he would have known that Kerry had to be squashed at every opportunity and not allowed to come back to life again. Of course, Clark was also a real threat. Such is the life of the most unusual frontrunner that has been seen in presidential politics for a while.
Iowa had a lot to do with it, but don't blame it all on Iowa...