In his new book, due out next week, Panetta says that by failing to respond, it sent the wrong message to the world. Obama said in August 2012 that if Syria used chemical weapons, that would be a "red line" for the US. But even after Assad used them, killing hundreds of Syrian civilians, Obama didn't take military action.
Panetta says it was a "blow to American credibility."
Panetta also chided Obama for not keeping a residual US force behind in Iraq, which he said could have helped stem the Islamic State group's recent takeover of parts of northern and western Iraq.