[BluffTHIS!]

I think that you are oversimplying things on both ends. The republicans are very good at party discipline, but what that means is that they work out their own internal differences behind the scenes. And maybe Bush has threatened to veto certain proposed legislation if it were not changed to suit him and we just don't know.

Also since history shows the party controlling the white house to do poorly in midterm elections, the repubs have a high priority on maintaining a common message and not appearing divided. This unity will allow them to pick up votes from the center from voters who might not like the repub policies 100%, but also don't like the discord that frequently characterizes the democrats' dealings amongst themselves. This can be readily seen in the fact that the democrats focus on saying NOT to whatever Bush is for, but can't among themselves agree on an alternative set of policies to present to the voters.