Sen. Kamala D. Harris (D-Calif.) and former vice president Joe Biden are re-litigating a decades-old civil rights issue: whether to use busing to integrate schools.

Busing became a major issue in the 1970s after the courts decided that communities weren’t appropriately self-integrating schools on their own, 20 years after the Supreme Court ruled to desegregate schools.

Busing became a focus in the 2020 presidential campaign after the first Democratic debate, when Harris attacked Biden for not being supportive of the type of busing that she participated in as a student. As Harris rises in the polls after that strong performance, she has an incentive to keep busing in the news — and Biden on the defensive.

But the more they bicker, the more their true opinions on busing get diluted and distorted. So let's review what, exactly, they support.

The bottom line is this: Harris says Biden opposed busing back then, which is mostly true. She supported it then, but doesn't explicitly support it now.

But both candidates are using the nuances of the busing debate to attack one another: There’s voluntary busing, involuntary busing, busing in the ’70s as compared with now. Here, the best we can gather, is where they really stand.

Biden opposed most busing in the 70s.

Overall, he did not think busing was a smart way to handle school integration. During the ’70s he called it a “racist concept” and an “asinine concept,” as The Post’s Chelsea Janes reports.

Harris’s campaign is circulating what he told a Delaware newspaper in 1975: “The new integration plans being offered are really just quota systems to assure a certain number of blacks, Chicanos, or whatever in each school. That, to me, is the most racist concept you can come up with.”

But now that Biden is under attack for his views, he’s splintered off aspects of busing he says he supported.

Now, Biden says that he supported voluntary busing or busing when it was mandated by courts in a community that particularly needed it.

On supporting court-ordered busing, here’s what he told CNN on Friday morning: “I was in favor of busing that was de jureing busing — that is if the court ruled that there was a law passed, or circumstances where a county, a city, a state prevented black folks from being somewhere — that’s wrong, you should bus. Well I even went so far in the middle of that busing controversy to say I’d use helicopters if that was necessary, to make the point.”

On supporting voluntary busing, he said during the debate that he opposed busing “ordered by the Department of Education.”

Harris supported busing when it was mandated by the federal government in the ’70s.

Unlike Biden, her position on busing back then is unequivocal.

“[T]here was a little girl in California who was part of the second class to integrate her public schools, and she was bused to school every day. And that little girl was me,” she said at the debate to Biden.

But Harris doesn’t support federally mandated busing today — unless society became as opposed to integration as it was in the ’70s.

"Busing is a tool among many that should be considered,” she said Wednesday.

Pressed by reporters on Thursday to clarify, she said: “If we got back to the point where governments were actively opposing integration, yes. I could imagine that would be when the courts would have to step in … I could imagine that, but thankfully that’s not where we are today.”

Busing may seem a rather anachronistic debate for 2020. While school segregation is still an issue in America, getting the government to order busing again is generally not the top priority for activists.

But consider busing a metaphor for this question: Who can best organize a coalition of black voters to beat President Trump? Black voters are a core constituency of the Democratic Party, and thus a key constituency to win the nomination.

Harris is using busing to make the case Biden isn’t supportive enough of civil rights causes, and his views are out of touch with today’s Democratic Party. Biden says busing is one piece of his larger civil rights record. Who’s making the best case? We’ll find out when voting starts in February.