Here’s where things got real. Van Jones, a former Obama staffer (and an African-American), turned to Mr. Lord and argued that Mr. Trump was “playing funny with the Klan” by not deploring them with the same passion he directs at other terrorist organizations. (Or for that matter, I’d say, Megyn Kelly.) Mr. Lord responded that Mr. Trump had said enough, that Democrats were “dividing people by race” and besides, the Klan was a “leftist” terror group.

Again: This is 2016. And here was a white panelist suggesting that his African-American peer should really go back and learn his history before criticizing someone about the Klan. Mr. Jones, calmly but with clear emotion, dressed Mr. Lord down: “We’re not going to play that game,” he said. “When you talk about the Klan, ‘Oh, I don’t know, I don’t know’ — that’s wrong.”

It was five minutes or so of the most stunning TV of the year. Even the body language was fascinating: Mr. Jones rested a hand on Mr. Lord’s shoulder at times, seemingly less as a dominating gesture than to keep the situation from spiraling out of control. (“I know you,” Mr. Jones said at one point. “I trust you.”) It was as if he were simultaneously battling Mr. Lord and trying to defuse a highly unstable bomb.

Cable debates typically end up with two parties yelling over trivia. The Jones-Lord argument was arresting precisely the opposite way: Two men were arguing, furiously but in control, over something dead serious.