He wanted to go. Badly. The easiest reads are Woodward.
He wanted to appear fierce, warlike and resolute. He wanted an attack fast, and he wanted it in Afghanistan.
I don't know where you get your information, but read Woodward and Tenet to start, then move on to Powell and when you are done I'll get you the names of a few others I've read.
He WANTED to attack Afghanistan as soon as possible. Political reasons.
There was enormous economic benefit to one of his greatest constituencies, the munitions manufacturers.