Let's not be changing history here. The Congress back the war, not because they were scared of loosing thier careers, but because they believed at the time it was the best course of action.
GW had good approvals then, because he reacted very well to the 9/11 attacks, remember he only had 50% of the vote to get into office... people were happy with his reation to the attack...
His approval rating now is down due to other issues, some he deserves the negative credit and some he does not fully.
Katrina is a good example. By past policies on disasters, cities are suppose to respond within 24 hours, the state within 2-3 days and the federal government within a week. The city of New Orleans dropped the ball, the state dropped the ball, and expected the federal governement to pick up all the pieces. Bush is partly to blame as he could have reacted faster, but somehow the city and state do not carry any burden of blame (though they share the majority of it).
Bush has been an easy target to stick all blame because he is so polarized. In that aspect he has failed as a president, as his leadership has not carried along public opinion... don't get me wrong, a president doesn't have to make policies that get huge approval ratings, but they have to make it up somewhere else... GW didn't do that...
In the same aspect, Obama is very polarized (in the opposite direction), and if he becomes the next president, watch and the same thing will happen to him... the one thing that Obama has going for him is that he is a better orator than GW... but the polarization will be Obama's downfall, as it was for GW.