Because the public is fickle, not to mention underinformed and stupid:
The poll shows that, since the surge is working, more people approve of the surge! Shocking how that works out. Of course, if the people had a chance to vote on it in the first place, it would’ve been shot down, Iraq would have been in chaos, and we’d be running out of the country with our collective tails between our legs and with a far higher body count.
We elect leaders to lead, not read polling data. Sometimes Bush’s stubbornness is a good thing.