Assad Responds to Obama: Syria Will Defend Itself Against Any Aggression

Kerry says blood and hair samples prove sarin nerve gas used in Syria, refrains from saying whether Obama would go through with military action if Congress rejects the president's request.

U.S. Secretary of State John Kerry said on Sunday tests showed that sarin nerve gas was used in a deadly Aug. 21 chemical attack near Damascus as he sought to build the case to convince skeptical lawmakers to authorize a military strike against the Syrian government.