This scenario has come up here before, and every time, there's always someone who is certain that the US will toss nukes hither and yon across the Islamic world. IMO, what you would be more likely to see would be a blitz of US special forces on known AQ training camps. The US public may be screaming for revenge, but the US government first needs information. I'd imagine that the US military will have a 'sovereignty be damned' attitude when it comes to AQ, and they will go anywhere they can to grab as many AQ people as possible. I imagine the war in Afghanistan will go much as it did in OTL, although perhaps with more US troops involved. Once they have some AQ people in hand and more information to act on, then you'd start seeing more overt military action; bombing strikes on known camps, out and out sniping down of AQ leaders and abettors, etc. While the US wouldn't go so far as to 'lose its soul' and toss nukes around, I would think that there would be a disregard for national borders ("if you harbor AQ people, expect a visit from us") and a lack of concern for those innocent people unfortunate enough to be living near AQ camps...