Glenn Snyder in his book on Alliance Politics does a great job of explaining the Alliance Dilemma--that relations with an ally are always a delicate balance because you want to assure them enough so that they support you when you need them but not too much that they drag you into a war you do not want.
Why mention this today? This post on Israel's potential plans for war with Iran. How does the US try to assure Israel that it will help Israel but not if Israel tries to sucker the US into a war it does not want to fight. One of the striking bits of this piece is how concerned/antagonized US military leaders are. They traditionally saw Israel as a key ally, reliable and impressive in its military history and ingenuity. Now, it is seen as a potential threat to American security because Israel might launch a war that leads directly to retaliation against US forces in the region and the deaths of American servicemen/women.
A few years ago, when Gen. Dave Petraeus was head of CENTCOM, there was a report that Israel's policies towards its occupation was a threat to US security by antagonizing the region. That is a bit less direct than an attack upon Iran leading to Iran attacking the US, but does show that the US military is losing its loving feeling for Israel.
The portion of the piece that deals with Chairman Dempsey's line that the US would not be complicit with an Israeli attack on Iran is quite sharp and illuminating. Again, complex signaling about US's support of Israel short of Israel dragging US into war. Check it out and ponder the challenges of allies (especially before Georgia gets to enter NATO).