President Obama now finds his administration occupied with three WMD -related crises: Iran, North Korea, and Syria. The resolution of all of them will depend in part on the credibility of U.S. threats and commitments, in this case the President's repeated statements that the use of chemical weapons would be a “red line” in his calculus about the possibility of a U.S. intervention.
As my Council on Foreign Relations colleague Jim Lindsay writes:
Do not threaten what you are not prepared to do. That is a cardinal rule of foreign policy. And it is a rule that is causing the White House diplomatic and political trouble now that it has agreed that Syria has likely used chemical weapons “on a small scale” against rebel forces.
It is not just the Syrian and other hostile governments who are watching, Lindsay argues, but our allies as well. Pressure now to intervene more heavily and visibly will be intense.
There are a couple of ways that Obama's red line could be parsed back, each of which carries problems. One is to say that it requires much more evidence than that so far underlying U.S., French, British, and Israeli assessments of sarin-gas use. A challenge here is that the Syrian government -- or its protector, Russia -- is well-positioned to block or at least slow any major UN investigative effort to validate the claims. (Perhaps a way to double-down on the red line in addressing this would be to make emphatically clear that such obstruction will be interpreted as confirmation).
Another way to parse Obama's threats is to interpret them as directed only at large-scale use, not isolated gas attacks. A danger here is that doing so might implicitly green-light continued small-scale chemical weapon attacks. One way of reading Assad's behavior to date is a gradual probing of U.S. threats for soft spots.