Worst case: world trade radicals. This would mean nobody to strike back at and would result in extreme loss of freedom for everyone as the "authorities" try to punish someone.

The Internet would be the first to go since that's where such groups coordinate their activities.

If it's the drug cartels, which I doubt, that would be rather messy and a lot of countries would end up hating Americans more.

If it's Ben Laden, that's a problem too. We can't bomb Afghanastan back into the stone age because the Taliban has already done that.

If it's Israeli radicals trying to make it look like it's Palestinians, that'll be messy too.

If it's Iraq or Iran, we have a major land war on our hands.

No matter what, this is going to be messy and a whole lot of people are going to get hurt one way or another.