Nikki Haley drew criticism this week for what she didn’t say. As she campaigned in New Hampshire for the Republican presidential nomination, a person asked her to name the cause of the Civil War.

Ms. Haley, a former South Carolina governor, joked it was not an “easy question.” She then mentioned “how government was going to run,” “freedoms,” the need for “capitalism” and individual liberties. When the questioner observed that she hadn’t mentioned slavery, she asked, “What do you want me to say about slavery?”

She told a radio interviewer the next morning that “of course” the war was about slavery, that she was not evading the issue but trying to reframe it in modern terms. While we shouldn’t read too much into one video clip, it’s fair to ask: How is the Civil War’s cause not an easy question?

The facts of our history are currently contested — especially that history. Gov. Ron DeSantis of Florida has acted to restrict what he sees as woke views of slavery and race in schools. Other Republican-led states have taken similar measures, and Donald Trump has offered his own hazy views of the past. It’s no wonder Ms. Haley spoke cautiously. The history of race has become as fraught a topic on the political right as it has been on the left.