George W. Bush may very well be the worst president in U.S. history. But Democrats are making a mistake if they try to pin all the blame for everything that is wrong with his administration on him personally. We should not focus so intently on Bush. Sure, he's exceedingly stubborn and unwilling to change even in the face of overwhelming public disapproval, but just replacing Bush with some other Republican is not going to make things better. In fact, it could make things much worse.
The real culprit that we are up against is the Republican governing philosophy. It has been especially awful under George W. because he had a Republican-controlled Congress for most of his presidency and was thus unfettered in his pursuit of Republican goals. Fortunatley, Bush's incompetence prevented him from fully achieving all of the Republican's goals, but we might not be so lucky if another Republican president is elected. Imagine how bad Ronald Reagan might have been had he not been somewhat constrained by a Democratic Congress.
Look back at the string of awful presidents we had during the early part of the 20th Century: Warren Harding, Calvin Coolidge, Herbert Hoover. Do you think that it was coincidence that we just happened to get three really bad presidents in a row? Not if you realize that it wasn't Harding, Coolidge and Hoover as individuals that were so bad, it was the Republican philosophy of making government serve the interests of big business and not regular people that made them so bad.
If we allow people to think that it was all Bush's fault individually they might conclude that there is no problem electing another Republican like Guiliani or Romney or Thompson, as long as it's not George Bush. But Bush was only a part of the problem, and a small one at that. Remember that Bush did fine as Texas governor mostly because he was following a conservative Democratic governing philosophy under the tutelage of Bob Bullock and Pete Laney. It was only after he jettisoned that philosophy in favor of a non-compromising partisan Republican one that started to spiral downward.