The Christian Science Monitor points out an inconvenient truth:
Perhaps one reason for this hesitancy is the fact that Israel, in a historic choice to rely on itself for defense, has never become an official US ally.
America has no treaty obligation [bold mine-DL] to come to Israel’s defense as it does with many countries in Europe and Asia. This little-known fact may loom large in a meeting Monday between President Obama and Israeli Prime Minister Benjamin Netanyahu.
I suppose it is a little-known fact, but it shouldn’t be. It’s fairly easy to find out which states the U.S. is formally obligated to defend. Every politician mentioning Israel feels compelled to refer to it as an ally, and the term ally is applied loosely to every client state that the U.S. has around the globe. Unfortunately, it becomes a lazy habit for everyone, including myself, to refer to U.S. allies when it would be much more accurate to call them clients, and this can create the false impression that the U.S. is required to provide the same assistance to our treaty allies and U.S. client states.
tbraton 
Chespirito 
“I suppose it is a little-known fact, but it shouldn’t be. It’s fairly easy to find out which states the U.S. is formally obligated to defend. Every politician mentioning Israel feels compelled to refer to it as an ally, and the term ally is applied loosely to every client state that the U.S. has around the globe.”
That didn’t prevent the leading newspaper in the U.S., the so-called “newspaper of record,” the New York Times from stating in today’s paper:
“Seeking to reassure a close American ally that contends it has reached a moment of reckoning with Iran, Mr. Obama rejected suggestions that the United States was willing to try to contain a nuclear-armed Iran. He declared explicitly that his administration would use force — a “military component,” as he put it — only as a last resort to prevent Tehran from acquiring a bomb.”
http://www.nytimes.com/2012/03/03/world/middleeast/obama-says-military-option-on-iran-not-a-bluff.html?_r=1&src=me&ref=world
If there is a slender straw to lean on, it could be the qualification about using force to “prevent Tehran from acquiring a bomb.” Couple that with the report last week that our intelligence agencies have concluded that Iran is not now seeking a bomb, and there might be some hope.