It was about proving it* to his father*, at least that’s how he explained it to himself. That meant, again in his own mind, winning his father’s war, the one his father stopped undone, and clearing some of the demons from his drunken wastrel 20’s and 30’s and all the comparisons to his father’s life that he got told about constantly. Again, it doesn’t have to make sense to be a reason.
None of any influence.
Since they had taken a strong position in urging Clinton to do it, even before 9/11, and came up with most of the lies told to support it, hell yes.
They thought it would be over in weeks and would pay for itself. They really did. What really happened was never considered possible, and those, like Shinseki, who warned them otherwise got expelled from school for it.