GWB is not as stupid as you think. And at the height of the 911 crisis, he easily enjoyed a 90%+ popularity rating.
Compared to Kerry, he was certainly the stronger and more determined leader. Americans deemed that GWB as their president could better protect their country from terrorist attacks, and thus they went ahead to re-elect him. By and large, GWB fulfilled that expectation of the Americans very well.
If you don't understand US politics, don't bother revealing your ignorance la.