Kamala Harris’ offensive against Joe Biden isn’t about busing, or segregationist senators, or gender or race. It isn’t about policy, really. It’s about two warring theories of how to win in 2020. And, not to get all Marianne Williamson on you, it’s about love.

First, the theories. The logic of Biden’s candidacy — the argument that he is the most electable of the Democrats — derives from one simple fact: A mere 88,000 votes across three industrial states cost Hillary Clinton the 2016 election. All the Democrats need do, according to his theory, is win those ballots in Michigan, Wisconsin and Pennsylvania that they couldn’t garner in 2016 — et voilà!

This scenario is especially attractive, because it doesn’t appear President Trump is in a position to win any new states from Democrats in 2020, which means his rival can focus on the three states like a laser beam.

By one estimate, 6 million people voted for President Barack Obama in 2012 and then for Trump in 2016; getting 88,000 of them back into the Democratic column shouldn’t be too much of a burden if you run a minimally competent campaign.

Still, the Democratic candidate has to have the appeal Clinton lacked. Trump won those votes by appealing to the white working class. Since Biden’s entire pitch as a politician is that he’s an amiable, ordinary white guy, he is the best candidate to achieve this simple goal.

It’s unimaginative. It’s boring. But it has the advantage of being a straightforward, simple and logical strategy.

No, no, no, say other Democrats: It’s a fool’s errand to chase these white working-class voters. The Democratic Party hasn’t won a majority of such voters since 1964. Instead, the Dems should rebuild what political journalist Ronald Brownstein called the “coalition of the ascendant,” which he defined as “millennials, minorities and socially liberal whites (especially college-educated and single women).”

Obama got 70 million votes from this coalition in 2008. Many of its members stayed home in 2016. Get them back to the polls in 2020, while adding more from the coalition who have grown into voting age, and Democrats won’t just win those three states back — they will utterly rout Trump.

In this respect, Harris is by far the best candidate on paper. At 54, she is relatively young. She is black. She is a she. She represents the most populous state in the union. But her candidacy wasn’t taking off — not until she confronted Biden at their debate and flummoxed him with her personal story of having been bused to Berkeley public schools.

That was important not because there’s anything to be gained from a discussion of busing, but because it gave Democratic voters some way to connect to Harris beyond her ­résumé — and because in winning in an exchange with Biden, she had implicitly made the case she could take the fight to Trump, too. And because it suggested she was someone they might come to love.

Every four years, we go through a national debate about whether people vote for candidates because they agree with their policy positions or because they have an emotional response to the person they’re voting for — admiration, respect or the feeling that the politician really understands them and what they’re going through.

You could call this “candidate of the head” versus “candidate of the heart.” What’s interesting about Biden’s candidacy is that it’s a candidacy of the head being run by someone whose viability is based in part on his already being a candidate of the heart.

As Obama’s veep, he was saluted by his boss in 2012 in words no president ever lavished on his running mate: “There’s nobody who knows more about foreign policy than my vice president. There’s nobody who gives me better advice than my vice president. There’s nobody who you’d rather have in a foxhole with you when it matters most than my vice president … I could not do what I do without him having my back every single day.”

And then, of course, there was and is the knowledge of the horrid tragedies Biden suffered and bore with extraordinary grace — the deaths of his wife and daughter in a 1972 car accident, the injuries his toddler sons experienced in that crash and, finally, the too, too early death of his son Beau in 2015 from cancer.

A senator best known for driving people crazy because he would never shut up turned into a beloved leader of his party. Now it looks like he is going to have to get lovable again — and fast.

jpodhoretz@gmail.com