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International crises are supposed to last days. Perhaps, like the Cuban missile crisis, they can stretch to weeks or, like the prelude to war in 1914, even months. But the Iranian nuclear crisis, which began with the revelation of secret nuclear sites in 2002, has now lasted a full decade. Although some might consider 10 years without war to be a success, it would be foolish to assume we can endure another 10. It is now more important than ever that we take advantage of fortuitous diplomatic circumstances and seek a deal with Iran, one which both addresses our basic security concerns and allows Iran to come away with dignity. The window for nuclear diplomacy between Iran and the west has been open since Barack Obama's re-election. But it will start inching shut as we approach the...