Proponents of action in Syria after the use of chemical weapons make a case — and it’s not a bad case — that the credibility of the United States is on the line.  Once the President draws a red line, we either need to back up those words or risk losing the deterrent our power provides to keep our enemies in line, and our friends confident of our protection.  With Iran still pushing to create its own nuclear-arms arsenal, that deterrent isn’t just a theoretical construct but a badly-needed reality. Advocates of action in Syria explicitly name Iran as the reason the US has to back up its red lines with action once crossed.

In this case, it’s instructive to see how we got to this red line in the first place. ABC News’ Devin Dwyer reminds us that this was an ad-lib gone horribly wrong:

While Obama has long spoken out against Bashar al-Assad and the use of chemical weapons, it was the president’s apparent off-the-cuff comments one year ago that may now be most responsible for putting the U.S. in a bind.

Obama’s warning in August 2012 that use of a “whole bunch” of chemical weapons would cross a “red line,” triggering “enormous consequences,” went much further than aides had planned, several told theNew York Times earlier this year.  Some reportedly wished Obama could have taken those words back.

Now, the Nobel Peace Prize laureate, who has made ending the wars in Iraq and Afghanistan his signature foreign policy achievement, is at risk of entangling the U.S. in a fresh Middle East conflict.

Dwyer refers to Obama as a “tortured spirit,” who never wanted to find himself in this position.  Even at the time, though, it was clear that Obama did want to put himself in this position — while hoping that Assad wouldn’t call his bluff.  Obama was in the middle of a presidential campaign which had begun to position him as the experienced foreign-policy hand, and the administration had spent the last few months bragging about its intervention in Libya.  Talking tough with Assad was designed to leverage his supposed success in Libya on the international stage as well as increase his standing at home, before the attack on our consulate in Benghazi exposed the disaster that Western intervention caused.

Dwyer even mentions Joe Biden’s bragging at the time, in the context of Obama’s sudden international isolation at present:

After the fact, Vice President Joe Biden declared the operation a new “prescription for how to deal with the world,” stressing “we don’t have to do it ourselves.”  “The NATO alliance worked like it was designed to do: burden sharing,” he told CNN.

Now, the loss of British backing of a strike against Syria is a significant blow to Obama’s vision, setting up two undesirable options:  not keeping his word on “enormous consequences” for crossing that “red line,” or going it relatively alone.

Last year, Obama put the US on the hook for another Libya-like intervention, based on a bet that Assad wouldn’t ever unleash his WMDs after seeing what we did to Moammar Qaddafi.  Assad must have seen what the real result was in Libya and guessed that we wouldn’t be dumb enough make the same mistake twice and hand another failed state to al-Qaeda and its affiliates.  This looks as if both nations made bad bets, and we’re on track for another war thanks to an impulsive ad-lib.  Small wonder the Brits chose not to double down.

Update: Matt Lewis says if we want to look tough to Iran, why not bomb them instead?