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Just over three years ago, acclaimed author and campaign adviser Samantha Power published a memo outlining the foreign policy Barack Obama would pursue if elected president. It was called “Conventional Washington versus the Change We Need.” Power’s argument—aimed straight at then-candidate Hillary Clinton—was that merely replacing George W. Bush with a Democrat would not truly change American foreign policy. It would not truly change American foreign policy because many of Bush’s policies had been supported by “the foreign-policy establishment of both parties,” which remained enthralled to a “bankrupt conventional wisdom.” Obama, she suggested, offered something different. As with his opposition to the Iraq War, he...