Arguing with James Fallow's contention that public saber-rattling against iran is counterproductive and we should leave the serious threats, if there are any, for back channels, Tigerhawk misses the major point. Not to misuse the holidays here, but think of the Exodus tale: The decidedly public, impressive plagues are repeatedly visited on the Egyptians, but each time Moses returns to the Pharaoh's antechamber, the wannabe demigod's heart is hardened (depending on how you interpret the passages, by God or by pride) and he ignores the latest plague, preferring to pit his society against divine wrath yet again. The end result, of course, is massive slaughter.
Our public projection of aggression creates some problems of that sort for the Iranian regime. Remember, first, that the Iranian government is not cohesive; it's fractured, with the populist maniac Ahmadinejad fighting for power against the Ayatollahs. His strategy? Nationalism. Persian pride. Every time America rattles its saber and declares what Iran can't do (which is obtain the same weaponry that America, and Israel, have), Ahmadinejad gets one more point in the polls. Each time that happens, he becomes more powerful vis-a-vis the Ayatollahs.
Now, in normal times, the Ayatollahs may judge the threat of American attack more compelling than the threat of opposing a broadly supported populist, but remember, Iraq has tied up our army, demonstrated our weakness, and made it look exceedingly unlikely that we'd risk a similar engagement against a stronger opponent. So they may gamble that America's bluffing, that it's all saber-rattling, and they should instead ensure they're not caught on the wrong side of Ahmadinejad's popularity. But we may not be bluffing. And therein lies the problem with such public threats: we make Iranian obstinance more popular, weaken those who could conceivably rein in Ahmadinejad, and risk a war borne from miscommunication. Don't believe that can happen? Read Guns of August.