If it is a ME terrorist, an Islamist, then there is a whole new and extremely tough set of problems that arise in dealing with it. And those problems relate to public reaction...which could run the gamut right up a sort of mini-civil war on our soil against muslims. There WILL be a majority public (non-Islam public) reaction and it isn't likely to be a reaction within the Kum-bay-a tradition. There may well be serious violence against muslim targets and individuals.
And the last thing the Administration wants is for things to boil over out of control domestically while we are fighting two additional external offensive wars.
Indeed, it would be an effective enemy tactic to bring the war to our soil in this manner -- those are the tactics that we use against our enemies (take the battle to his home). I think this is what the Administration is attempting to avoid if they can.
But if the truth is as we expect they might need to reconcile themselves to much harsher internal measures against Islamist targets while they fight offensively against both Al Qaeda and Iraq (Al Qaeda's storehouse). But that ratchets up the degree-of-difficulty a great deal.