In comments at the Dean2004 blog, Jerome Armstrong makes a good point about Ridder’s departure:
A few months ago, the campaign realized they had the wrong campaign model. Last year, it looked like it was going to be a three-state contest, with IA, NH, and SC deciding the nomination. Along those lines, Ridder was the one of those who had the ground experience to hire a staff of 50 in each of those states, and run the campaign in such a mode.
Everything changed with the primary shake-up, and it’s become a national campaign much earlier. Hence, Trippi and Binder taking a much earlier leading role in the campaign than initially mapped out.