Some Iranian reaction would be inevitable -- from encouraging Hezbollah in Lebanon to rain missiles down on northern Israel to more limited efforts. While most hope Iran would be restrained, there's a chance of a major regional conflict that could draw in the US and countries in the Persian Gulf and send oil prices soaring.

President Obama's administration insists that "all options are on the table" regarding Iran's nuclear program, but is strongly opposed to unilateral Israeli action, not least because it would put US troops in Afghanistan and Iraq in harm's way.

Iran has cultivated militant groups in both countries and could increase the number and lethality of weapons it provides them in response to an attack -- which most of the Muslim world will see as having been approved by the US. That would not only complicate US efforts to extricate itself from its two current wars, but also shatter US public standing in the Muslim world.

An attack would also boost hard-line Iranian President Mahmoud Ahmadinejad and his circle, generating a 'rally around the flag' effect that would further undercut the opposition and increase his standing in the broader Muslim world.