Remember the line from Peter Pan about a fairy dropping dead when anyone said "I don't believe in fairies"? Even though he stirs up the fighting spirit among liberal stalwarts, every time Howard Dean says "I hate Republicans" another "D" voter drops into the "R" column.
It may not really work out that neatly, but the Democrats' failure to capitalize on Republican woes can only be attributable to the actions of the official "D's" themselves.
So that is why I think it is a good thing that Republicans are fighting against each other. Democracy thrives on friction and the opposition party can't muster anything but limp histrionics. So the fight goes on between Right and Center-Right and their various combinations.
Here is an interesting take on this fight. Ryan Sager dismisses the Left's hopeful comparisons of 2006 to 1994, saying that it is shaping up to look more like 1998.