Imperfect but forgiven
The most our government should have done was a brief military incursion into Afghanistan, preceded by an intense bombing mission to soften the target. But that's not what happened. Twenty years of war, thousands of lives lost, billions of dollars wasted, a innumerable number of people hurt, displaced, depressed -- and with nothing to show for it.
Since we were attacked on our own soil, I think we should have driven alkaeda and the taliban into the mountainous caves where they hid and then used nukes to erase all life in that area...and we should have advised pakistan that if we found any evidence of Pakistan colluding with Alkaeda going forward, we'd treat them similarly.