As far as I'm concerned the war with Iran isn't if, but when. It's as inevitable as tomorrow's sunrise. Hell, it may even come with tomorrow's sunrise.
Israel will most likely strike first as they must.
If Israel attacks, Iran will retaliate with a massive pan-regional tantrum especially since its proxy, Syria, is all but crippled by internal strife. That greatly hinders its conventional response, i.e. Hezbollah.
So Iran will lob a Whitman's Sampler of missiles across the Persian Gulf. Shipping and minor Gulf Arab states will be the likely candidates. No doubt any attack by Israel will be assumed to have occurred with the tacit if not explicit permission of the US. US naval forces and forces in Afghanistan will be subject to attacks from conventional missiles. Once that happens a larger war will commence...unless the president levels an overwhelming response.
Obama knows this.
He doesn't want a larger war, especially when half of his appeal to his base rests on his "ending" the Iraq war and drawing down in A-stan.
If Obama doesn't want a larger war his best shot is to prevent the attack by the Israelis.
Israel is pretty much already deadset on not telling us if and when they will attack. While they did not share with us prior to their attack on Saddam's Osirak reactor in 1985 they have all the more reason not to trust the WH.
So...
...suppose we detect multiple Israeli aircraft and missiles streaking towards Iran?
What are the odds that Obama would order US carrier aircraft and other airborne assets to intercept the Israeli attack so that he can claim he kept us from another, larger, regional war?
Sure, many here would be furious but this is the man that coordinates with Media Matters where "Israel-firsters" are coonsistently attacked. He doesn't think like us in terms of allies but in some grand theoretical scheme that says if the US would only do more to assuage the grievances of others there would be more peace in the world. The protest of his detractors will never figure into his calculations.
Would he, at a minimum, try to warn the Iranians even if it meant sacrificing highly classified sources and methods to convince the eternally suspicious mullahs of his sincerity?