Who would have thought? A demented 21-year-old troll named Dylann Roof, accused of killing nine parishioners at a historic black church, has turned history upside down. Roof’s attachment to the Confederate battle flag has set off a dramatic reconsideration of how we remember the Civil War.

For example: 

■  Yale University may rename its venerable Calhoun College. Senator John C. Calhoun was the famous white supremacist whom historian Richard Hofstadter memorably called “the Marx of the Master Class.”

■ The finger-in-the-wind leaders of the Democratic Party are abandoning their tradition of Jefferson-Jackson dinners, rubber chicken meetups named for Thomas Jefferson and Andrew Jackson, great presidents who happened to own slaves.

■ There are moves afoot in Maryland to take down statues of native son Roger Taney, the chief justice of the Supreme Court who authored the 1857 Dred Scott decision that denied citizenship to black Americans.