I think we ALL know the answer to that?
I'm actually not convinced Israel will launch such an attack. At least I hope not. I shudder to think of the consequences of what that will mean for the Middle East, America and the whole world. The possibility of Israel successfully significantly downgrading Iran's nuclear program or their military capabilities is minimal. They simply don't have sufficient long-range resources. Even the Pentagon who do have several times more resources and the aircraft carriers and facilities on Iran's doorstep doubt that an attack by the U.S. would be successful at sufficiently downgrading Iran's nuclear program or their military capabilities. Furthermore, the instability on the Gulf caused by such an attack and the probable side effects of an attack would be so dire I'm quite certain the U.S. would use its influence to try to stop it.
But if I am wrong and Israel does attack Iran - does anyone have any doubt about what the public position will be of vast majority of Democrats in Congress as well as the Obama White House? Any doubts at all?