In my opinion the United States and United Kindom are there for the purposes of mitigating any damage from "massive retaliation" coming from the hostile states and enemy agents within friendly states to Israeli actions against OUR enemies. Our reasons to be there are both agressive and defensive. Regardless what you feel or believe about the economic and religious orgins of this conflict you have to recognize that threats to Israel do not and WILL NOT stop in Israel. Virtually to a man, Islamic radicals contend that there is no distinction between the Zionists and the US and UK. That's the one precept under with they all operate.
To get to Israel Iranian forces now have to contend with a substantial military force that has had many years on the ground to measure the battlefield and dig in for the inevitable confrontation. The "Coalition of the WIlling" isn't stumbling blind in the desert in spite of the public's perception of abject failure in Baghdad. I'm convinced that Iraq is nothing more than a military base that our present leaders (Democrat and Republican) think we need. It was an easy target, at least the "Mission Accomplished" portion. They are willing to sacrifice soldiers and innocent Iraqis there for the sake of larger goals in the region. Remember Earnie, I'm not passing moral judgement here. These are my predictions, observations and estimations of the competing forces.
Remember how Muhammad Ali used to stumble and fall back against the ropes after his opponent connected with a solid blow.
Absorbing headblows was a mighty foolish game plan but boxing experts agree that seldom was there any urgent weakness behind his "Rope a Dope" tactics.