Historians and the history-minded began having persistent Reconstruction flashbacks even before last week, as Democrats discussed how far to take the many possible future investigations and prosecutions of Donald Trump. With the Capitol riots and related events of Jan. 6, those flashbacks got more vivid. Would stronger punishments for the figureheads of secession have worked? I asked Cynthia Nicoletti, a historian at the University of Virginia who wrote a book about why the North failed to bring the leader of the Confederates to trial (Secession on Trial: The Treason Prosecution of Jefferson Davis), to explain how Southerners who led the rebellion managed to escape punishment and to speculate as to whether that move might have made a difference. Our conversation has been edited and condensed for clarity.