If you're having trouble keeping track of all the promises, threats, and "red lines" that Obama has applied to Syria and Assad, you're not alone. There have been so many that things tend to get confusing. However, one constant through it all has been a warning that, if the Assad regime uses chemical weapons, it would trigger a US military response.
Now we have widespread reports of the Assad regime deploying weaponized chlorine gas. So, if you're a President who's absolutely terrified of backing up his own proclamations with actual action, what are you to do? That's right. You move the goalposts.