I think Obama's biggest failure was Libya. The US should stop supporting rebellions, or invading countries. It's never clear what's going to happen when the revolutionaries take over, or the new regime is in place, and the war itself is always bad.
IIRC, that was Nicolas Sarkozy's idea. Obama's fault is that he joined him.
Back in mid 1990s USA and the whole Western World was heavily criticized for not intervening in Rwanda conflict and many people in the US and Europe took that criticism to their hearts and now they tend to err in an opposite direction.
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