If Bashar Assad faces the choice of winding up like Saddam and Gaddafi or gassing his own people, what decision do you expect him to make, knowing what you know of his character?

Obama’s punitive strike won’t deprive Assad of his weapon or change his survival calculus. What the attack will do is change the calculus for rebel groups everywhere that would like to enlist U.S. cruise missiles in their cause. All they’ll have to do in the future is stage an Aum Shinrikyo-style gas attack and blame it on whatever government they’re attempting to overthrow. What’s more, each time a dictator like Gaddafi or Assad falls, his chemical weapons don’t just disappear—they wind up in the hands of a new, equally untrustworthy regime, and amid the chaos of a regime’s collapse they have the potential to find their way into the arsenals of non-state actors.

There’s a reasonably good chance that chemical weapons will be used again in Syria after Obama’s attack (assuming he gets his way with Congress). What then? More symbolic remote-control killing of Arabs—or will Obama accede to the pressure John McCain is already putting on him to “finish the job” with regime change? In that case the brightest scenario is one that looks like Libya, only with the U.S. not (wisely) leading from behind but playing the primary role in toppling the Assad regime. Libya doesn’t exactly make most Americans feel warm and fuzzy these days.

And if an attempt at regime-change-by-airpower fails, then do we invade? Does the president back down at that point, once he’s already raised the stakes and thereby lost more “credibility” than is at risk in this month’s congressional vote? If Bill Kristol and James Ceasar are really concerned about presidential credibility, they had better hope Congress tells Obama “no” before this train even leaves the station.

There’s no danger to the U.S. in not going to war with Syria. There are grave dangers, of an escalating nature, if the U.S. does go to war. The principle of discouraging chemical-weapons use cannot realistically be supported through the means Obama proposes—but certainly it can be undermined in this way. The president has never articulated a clear foreign-policy vision; he’s run hard up against the impossibility of reconciling his vaguely antiwar leanings with the realities of U.S. power. Now he’s made a mistake in proposing a war that he cannot, on several strategic levels, win. His best course is to stop before the shooting begins. This isn’t the way to control WMD, and Obama isn’t prepared to pay the consequences of failure.