Adjusting his own views on engagement, Roger Cohen thinks that now is the time to isolate Iran:

Obama must leave [Khamenei and Ahmadinejad] dangling for the foreseeable future. He should refrain indefinitely from talk of engagement. To do otherwise would be to betray millions of Iranians who have been defrauded and have risked their lives to have their votes count. To do otherwise would be to allow Khamenei to gloat that, in the end, what the United States respects is force. To do otherwise would be to embrace the usurpers. The slow arc of moral justice is fine but Iran is gripped by the fierce urgency of now. Obama, the realist on whom idealism is projected, is obliged to make a course correction.

I say all this with a heavy heart. Non-communication between America and Iran is bad for both countries and the world. It complicates and undermines every U.S. objective from Gaza to Afghanistan. It’s dangerous and it’s unnecessary. I’ve argued strongly for engagement with Iran as a game-changer. [...] But the Iran of today is not the Iran of three weeks ago; it is in volatile flux from without and within. Its Robespierres are running amok. Obama must do nothing to suggest business as usual. Let Ahmadinejad, he of the bipolar mood swings, fret and sweat. Let him writhe in the turbid puddle of his self-proclaimed “justice” and “ethics.”

I'm wrestling with this question, and haven't yet made up my mind. My heart certainly belongs with Roger Cohen on this. My head is still trying to think it all through. My thoughts over the weekend are here.

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