Mounting evidence of reported chlorine attacks in Syria could renew talk of military action any day now.
Human Rights Watch says there is "strong evidence" of multiple chlorine attacks in Syria last month, with clouds of yellow gas killing 11 people and sickening another 500 with symptoms that can include vomiting, splitting headaches and uncontrollable coughing.
And now U.S. President Barack Obama who said he "will not tolerate" the use of chemical weapons faces another challenge to his red line – one that will again test his credibility, and renew talk of U.S. military action in Syria.