Even in light of recent evidence that Syria‘s embattled ruler, Bashar al-Assad, might have used nerve gas against his own people, Barack Obama seems reluctant to escalate American involvement in Syria’s brutal civil war. But another scenario involving chemical weapons could force Obama into the deeper engagement he has long resisted: the alarming prospect that radical Islamists could acquire Syrian chemical weapons and try to use them beyond Syria’s borders, perhaps even within the United States. “I think we should be worried,” says Jeffrey White an analyst at the Washington Institute for Near East Policy and former military intelligence officer....