Weirdly, it was Marianne Williamson who kicked off the most riveting moment in two nights of Democratic debate.

Shortly after Rachel Maddow and Chuck Todd took over as moderators at the halfway point Thursday night, the spiritual guru and author made this provocative statement (possibly the most sensible thing she said all night):

“The average American is woefully undereducated about the history of race in this country.”

Like kerosene on a small blaze, this set off a conflagration. Candidates shouted over each other, all wanting a piece of that hot topic.

Kamala Harris broke through the babble. Clearly, she had something to say and she was going to say it. If it meant playing a card that only she held, what more appropriate time — and who could argue?

“As the only black person on this stage, I would like to speak about race.” This seemed to part the roiling waters for a crucial second.

Maddow (whose instincts and demeanor were excellent on both debate nights) tried to set a limit, perhaps knowing that was impossible.

“Go for 30 seconds,” she directed the senator from California.

The Washington Post's Dan Balz analyzes Sen. Kamala D. Harris's (D-Calif.) breakout moments during the June 27 Democratic primary debate.

Harris seemed unhurried, though, as she began her softly brutal attack on former vice president Joe Biden.

She launched into a prepared, but still emotionally stirring, story about being a child who was bused to public school — one who might easily have been affected by anti-busing efforts promoted by the kind of segregationist lawmakers whom Biden had recently touted himself as able to work effectively with. And, she said, Biden himself had opposed federally mandated busing programs.

NBC played the episode wisely.

Moderators backed off, letting the moment unfold, and the network provided the one absolutely necessary element: a split screen.

On one side, there was Biden’s face as he absorbed the brunt of what was coming at him, and on the other, Harris as she delivered what she came to deliver — a deeply personal story about a child growing up amid racial politics.

“There was a little girl in California, part of the second class to integrate her public schools and she was bused to school every day . . . ”

Then came the line that will be remembered.

“That little girl was me.”

Moments later, underlining just how planned and strategic a move this was, her staff tweeted out a photo of the schoolgirl-age Kamala Harris: serious-faced, dressed in a white blouse and neat coat, with her hair in pigtails.

When it came time for Biden to respond, it was Chuck Todd’s turn to set a limit. “30 seconds,” he said.

Biden counterpunched effectively, saying Harris had mischaracterized his position and then going right for her weak spot: “I was a public defender. I didn’t become a prosecutor.” (Harris has been reasonably criticized for elements of her longtime role as California attorney general — policies and decisions that supported law enforcement over the interest of criminal defendants who were often people of color.)

Applause swelled for Biden, and the fiery exchange was allowed to continue, with the moderators admirably quiet.

On his heels, the former vice president eventually trailed off by suggesting that he had already used up his time — a sound bite that is sure to be replayed constantly by those who want to show that at 76 he’s long past his prime.

Journalist Rebecca Traister, author of “Good and Mad: The Revolutionary Power of Women’s Anger,” tweeted later: “I am still thinking about six minutes ago. Harris directly confronting Biden on busing/segregationists was historic, powerful, and unimaginable on a presidential stage until very recently, which is itself symptomatic of a world Biden is struggling to defend.”

The moment would linger in memories for far longer than six minutes.

Late-night host and comic Trevor Noah unpacked the moment later on his Comedy Central show: “At this point, Kamala was busing Biden right out of the debate. She was killing it.”

And, Noah quipped that it was a moment that reminded him about “why you have to love black women. You think they have forgotten what you did, and out of nowhere, they will spring that s---.”

2020 Democratic presidential candidates went head-to-head on a number of issues during the first Democratic debate. Late-night hosts had a lot to say.

After the debate broadcast, conversing on air with MSNBC anchor Brian Williams, Maddow reflected on the many topics that moderators regretted that they didn’t have a chance to get to.

But that was unavoidable, she said: “A lot of stuff tonight needed to breathe.”

The two nights of debates were, overall, something of a trial for those viewers who were interested in educating themselves about the 20 candidates’ character, personalities and policies.

At their worst, which was most of the time, the four hours were dismissible, overcrowded, annoying shoutfests.

But every once in a while, a televised debate can allow for moments that matter — not just viral put-downs or dumb gaffes, but defining moments. Even unforgettable ones.

This, indisputably, fit that category.

And NBC deserves real credit for not getting in the way by enforcing rules that were made to be broken.

For more by Margaret Sullivan visit wapo.st/sullivan