GWB did a pretty decent job in uniting USA after 9/11.
He made some disastrous decisisions, and you can't say that it was Dick Cheney's fault or Karl Rove or anyone elses. Because the president has the ultimate responsibility.
So he is responsible and one of the worst presidents ever.
Eg, look at what he did with a booming economy at hands. Never balancing the budget. Only expanding the deficit.
But regardless - GWB did a good job keeping the nation united the weeks following the 9/11.