In response to our support, Iran would retaliate against us, probably domestically by hitting the electrical grid or something similar. Ahmedinejad would explain this retaliation to the American people as being in response to our support of Israel. He would assure us that if we were to simply mind our own business, Iran would leave us alone. This is consistent with the Qur’an*:
9:29 Fight against such of those who have been given the Scripture as believe not in Allah nor the Last Day, and forbid not that which Allah hath forbidden by His messenger, and follow not the Religion of Truth, until they pay the tribute readily, being brought low.Note that Ahmedinejad has previously offered us the Scripture, in his invitation to George Bush.
Iran could keep up low-level attacks indefinitely by the use of stateside Muslim groups. My impression is that a President Obama would sacrifice Israel.
*until, of course, we face our own decision of conversion, subjugation, or death a few decades down the line.