There are still nearly two years left in Barack Obama’s presidency, but historians looking back on his record in foreign policy will surely identify one costly error: his refusal to follow through on the implied threat in stating that the Syrian regime’s use of chemical weapons would be a “red line.”

That statement was made in a press conference on Monday, Aug. 20, 2012. The president was not scheduled to appear; press secretary Jay Carney said, “Looks like there’s a surprise guest here.” After fielding questions on other topics (Missouri Senate candidate Todd Akin, Mitt Romney’s attack ads and tax returns, friendly fire deaths in Afghanistan) Obama responded to NBC’s Chuck Todd’s question on whether he envisioned using U.S. military to keep Syria’s chemical weapons in safekeeping.