Forty-five years ago, on a sunny Friday afternoon, I walked into a physical education lecture hall at Cole Field House, in College Park, where a squat, crew-cut instructor named Fluke, having heard the first sketchy radio bulletins about a shooting somewhere in Dallas, tried to sneer in the face of history.

“Everybody just sit there,” he ordered that classroom full of University of Maryland freshmen. “I’ve got a lecture to deliver. When I’m done, then you can go find out whether or not the president’s dead.”