Ted Widmer, who was a speechwriter for President Bill Clinton, is the director of the John Carter Brown Library at Brown University and the author of “Ark of the Liberties: America and the World.”

ON June 12, 1987, the cold war entered a terminal phase, in ways that few could have anticipated, and in fact, almost no one did — with the exception of a president down on his legendary luck.

If in 1984 Ronald Reagan had proclaimed that it was “morning again in America,” three years later the evening was coming fast for a presidency that had spent most of its energy. The Iran-contra scandal had damaged him, and in March 1987 only 42 percent of Americans approved of the job he was doing. Reagan’s diary reveals a president losing focus, with entries registering more enthusiasm for old videos than the crushing business of state. On May 23, 1987, a good day: “Ran a movie about Big Foot & to my surprise I was in it — a shot of me & Bonzo on a TV set.”

But the aging actor still had a trick or two up his sleeve. For months, a trip had been planned to Berlin, a city famous for its stages. John F. Kennedy had given one of the greatest speeches of his presidency there in 1963; it would be a challenge for Reagan to duplicate the excitement of that visit. Like him, the cold war seemed to be losing steam. But Reagan’s loyal aides pitched the idea of a major speech at the Brandenburg Gate, and the writers began to crank out drafts. A single line kept calling attention to itself: an appeal to tear down the Berlin Wall, which ran alongside the gate....