Obama’s credibility — and that of the United States — is draining away as well. Assad has been subtle about testing America’s “red lines,” gradually escalating his use of missiles and airstrikes against civilians, and now slowly introducing chemical weapons. It was always incongruous of Obama to specify the use of chemical weapons as a “red line,” as if the deliberate slaughter of innocents on such a scale could be allowed a pass. But, once such weapons were used, Obama compounded the error by inserting not one but two qualifiers into his denunciation of the regime: It was the “systematic” use of chemical weapons against “civilian” populations that would not be tolerated, he declared. What message would Assad and his generals have heard in the presidential palace in Damascus? That the occasional use of chemical weapons, or even the systematic use of such weapons against the rag-tag Free Syrian Army, would be fine. Obama’s red lines, as Sen. John McCain said over the weekend, appear to be written “in disappearing ink.” Tehran, Moscow and Beijing will have heard that message clearly.

Syria may not have been high on Obama’s agenda for his second term, but how he reacts to this new escalation will have repercussions for U.S. policy far beyond the Levant. Not intervening in Syria as civilians die of chemical attack could be as bad for America under Obama as intervening spuriously in Iraq was for George W. Bush.