It would be a grave error for the Democrats to nominate a candidate favorable to the stances of their radical left-wing. That is the one thing that could drive moderate voters who are tired of Republican rule back into the arms of the Republican party in the election of 2008.
I have come to the conclusion, after observing human and political behavior for the past half-century, that there is an attitude, deeply engrained in our natures which says "NeverneverneverEVER admit a mistake or yield a point to the opposition because to do so is to admit one's own fallibility."
Thus, we see the same political mistakes being made, time and time again, by both Democrats and Republicans....and a widening gulf between the two parties and their supporters.