Bush is doing what he thinks is right -- and more than three out of four Americans agree with him. No "wag the dog" here... We're the "good guys" in this fight (and in this world), and no one has _any_ evidence to the contrary. Our (US, UK, Australians, Poles, Spaniards, and a few others') troops are laying it on the line for the freedom of others; that's unique, historic, and heroic, boys and girls!
If it were about oil, we wouldn't be rolling the dice on a new democratic government in Iraq -- we've been getting cheap oil in the ME for years, and it would have been even cheaper if we'd just lifted the sanctions on Iraq and let Saddam have his way for another 30+ years!