Jon Grinspan studies the especially rage-driven time in our political history between the end of the Civil War and the year 1900 or so. It may seem contradictory, but focusing on the political pessimism of our past actually makes him rather optimistic.

“The thing I find optimistic about studying this era is that you see that it ends,” says Grinspan, who is a curator of political history at the National Museum of American History. The New York Timescolumnist David Brooks interviewed him on stage at this year’s “The Long Conversation,” an annual event that brings together more than two dozen thinkers for an eight-hour relay of two-person dialogues at the Smithsonian Arts and Industries Building.

For Grinspan, becoming a historian was a portal into human empathy. When he comes across an old document describing a stolen election or a riot, he is really overwhelmed by the sense that Americans were able to confront frustrations with their political system and resolve them. ...