What's the worst foreign policy/national security mistake that Barack Obama has made? By "worst" I mean the one with the most important consequences, so I'd also like to know what you think it has major effects.
(And technically: I'm asking for the worst mistake by the US government, or at least the presidency/exec branch, during the Obama presidency. It's always difficult to know, especially in this realm, which are presidential decisions and which are not. But the shorthand is okay most of the time).