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Wendy Sherman was on the verge of tears. It was July 2015, and Sherman, then a top Obama administration official at the State Department, had just stepped up to a lectern in a drab conference room. The tears, Sherman reassured her rapt audience, were “largely exhaustion.” She had flown back to D.C. the night before from Vienna, where she had led the U.S. delegation that successfully negotiated the Iran nuclear deal. Now, just hours after inking arguably the most significant arms-control agreement of the 21st century, Sherman was on hand to answer questions from a roomful of suited, youngish people attending an annual State Department conference about nuclear policy.

I was one of the suited, youngish people in Sherman’s audience. A rising junior in college, I had wandered into the nonproliferation conference—as one does when one goes to school in the nation’s capital—in hopes of seeing a favorite professor, who was set to give a lecture on nuclear history. But Sherman’s return after clinching the Iran deal had forced a change to the schedule. And as she stood there blinking back her emotions, Sherman told us a story that I’ve been flashing back to ever since Donald Trump started his war with Iran—one that now reads like a relic from a more hopeful political era.

Sherman, wearing a tan pantsuit and dark-framed glasses, recounted what had happened the previous day. Negotiators from the U.S., Iran, and the other five countries party to the deal had gathered at a United Nations complex on the banks of the Danube to speak privately about the agreement they’d just reached. The diplomats, Sherman explained, sat in a horseshoe formation and spoke one by one. U.S. Secretary of State John Kerry went last, and he initially stuck to his talking points. But then the mood shifted. “At the end of it, Secretary Kerry, completely impromptu, said, ‘When I was 22, I went to war,’ ” she recalled, referencing Kerry’s tour of duty in Vietnam in the late 1960s in which he was repeatedly wounded. “And then he choked up, sort of like I did a few minutes ago. He couldn’t get the words out. And everyone was completely spellbound.” After the secretary regained his voice, Sherman went on, he managed to complete his thought: “I went to war, and it became clear to me that I never wanted to go to war again.” Sherman then summed up the lesson for the conferencegoers hanging on her every word. “That’s what this was all about,” she said of the Iran deal, “trying to settle these matters through diplomacy and peaceful means. And it was such a moving moment that everybody in that small room applauded, including the Iranian delegation, and everyone had tears in their eyes.”

You can watch a video of the speech Sherman gave at that conference 11 years ago here. Viewed from a very different moment in U.S.–Iran relations, it becomes a window into an alternate history, a glimpse of what’s been lost to two Trump presidencies. The Iran nuclear deal, reached during the twilight of the Obama administration, grew out of a distinctly Obamaesque ethos: that professional, expert-informed, diligent diplomacy with allies and adversaries alike could yield progress on seemingly intractable problems.

Landing a few years after that administration had sealed a major U.S. arms-control agreement with Russia and amid its detente with........

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