First, there's the bare bones legality of it:
First, in the absence of an imminent threat (and the Iranians are at least several years away from having a nuclear arsenal), the attack would be a unilateral act of war. If undertaken without a formal congressional declaration of war, an attack would be unconstitutional and merit the impeachment of the president. Similarly, if undertaken without the sanction of the United Nations Security Council, either alone by the United States or in complicity with Israel, it would stamp the perpetrator(s) as an international outlaw(s).Next, it would complicate an already dangerously deteriorating situation in the Middle East.
Second, likely Iranian reactions would significantly compound ongoing U.S. difficulties in Iraq and Afghanistan, perhaps precipitate new violence by Hezbollah in Lebanon and possibly elsewhere, and in all probability bog down the United States in regional violence for a decade or more. Iran is a country of about 70 million people, and a conflict with it would make the misadventure in Iraq look trivial.Third, it would hit us (and everyone else) in the wallet as much as it would on the war front.
Third, oil prices would climb steeply, especially if the Iranians were to cut their production or seek to disrupt the flow of oil from the nearby Saudi oil fields. The world economy would be severely affected, and the United States would be blamed for it. Note that oil prices have already shot above $70 per barrel, in part because of fears of a U.S.-Iran clash.And last, it would exascerbate the terrorism problem just as the misadventure in Iraq has done.
Finally, the United States, in the wake of the attack, would become an even more likely target of terrorism while reinforcing global suspicions that U.S. support for Israel is in itself a major cause of the rise of Islamic terrorism. The United States would become more isolated and thus more vulnerable while prospects for an eventual regional accommodation between Israel and its neighbors would be ever more remote.As we so often say, read the whole thing. This draws a stark picture about as clearly as you could wish. Congress needs to get a very short leash on the madmen in the White House as quickly as possible.