Trump has made his choice. Like he did with the Supreme Court, the Paris Climate Accord, and the U.S. embassy in Jerusalem, Trump kept a promise made many times throughout the campaign. In truth, anyone who has listened to Trump over the last several years should not be surprised by his decision. From the beginning, he understood that any deal which gives the weaker party benefits up front in exchange for minimal temporary concessions is not a deal worth taking. And since he does not accept the worldview that inspired the deal, there is no reason for Trump to remain in it.
The worldview Trump opposes privileges therapy and dialogue over realism and hard decisions. It imagines that the Iranian theocracy is a reliable or trustworthy hedge against Sunni power and will liberalize gradually as the arc of justice progresses. These are the ideas that motivated the presidency of Barack Obama. The Iran deal was the signature achievement of Obama’s second term, and it is now gone. In truth, though, Obama’s legacy was disappearing long before Trump made his announcement. Obama’s legacy, like much of his self-presentation, was a mirage, a pleasing and attractive image that, upon closer inspection, loses coherence.