Harris has lately earned mockery from the right for rambling incoherently, as she did at a White House event for Women’s History Month in March. Clips like this will play on a loop next year, when you can expect to see constant reminders of Biden’s frailty. Nikki Haley got the ball rolling when she predicted that Biden wouldn’t live another five years, and that “if you vote for Joe Biden, you really are counting on a President Harris.”

Not a tasteful message, but not necessarily ineffective, either. The subtler version would be: “A vote for Democrats might be a vote for Biden. But then again, it might not.”

All of this illustrates a central truth of presidential politics, which is that calculations made in the throes of a campaign always exact their consequences down the road.

Because to understand the root of Biden’s Kamala Harris Conundrum now, you have to understand his thinking in 2020 — which means touching on fraught subjects of race and gender. (This is a thankless task in the current environment, but let’s do it anyway.)

Having publicly promised to choose a woman during his primary campaign with Bernie Sanders, and then wanting to hold his party together during an agonizing summer of racial unrest, Biden determined that his running mate should be a Black woman. It was the right call at the time, morally and politically — although I would argue that by publicly crowing about his criteria, Biden’s campaign did his eventual running mate a disservice, ensuring that whomever he chose would be seen as the best Black female candidate rather than the best candidate, period.

Given the country’s long struggle with inclusivity at the highest levels of politics, however, the list of Black women with obvious credentials wasn’t long, and most of the candidates were untested.

The safest choice, by far, was Harris. She’d been elected statewide in California, and she’d already been introduced to the country as a presidential candidate. With at least as much experience in public life as Barack Obama had when he ran for president, and far more than Donald Trump, Harris was always the most obvious fit.

But 2024 will be a very different election from 2020, and now the bill for Biden’s political calculus may be coming due. Democrats defend Harris or insist that running mates don’t matter in a presidential campaign anyway, and usually that’s true. (I’d argue that Sarah Palin mattered in 2008, although she was less of a running mate than a running gag.) But Biden is four years older now, and with Republicans already harping on the president’s mental fitness, Harris will face more scrutiny than any running mate we can remember. Her favorability ratings have closely tracked Biden’s, but they’re consistently lower and well below those of other recent vice presidents.

Even Harris’s allies are hard-pressed to make the case that she’s had much impact in office (although, really, it’s hard to find vice presidents who do). In a recent New York Times opinion piece, plaintively titled “The Excellence of Kamala Harris Is Hiding in Plain Sight,” the Democratic strategist Donna Brazile summed up Harris’s record, in part, this way:

“Ms. Harris has pushed for federal legislation to secure voting rights, worked to expand access to the child tax and earned-income tax credits, is co-leader of the White House Task Force on Worker Organizing and Empowerment, was an integral part of the White House’s push to get Americans vaccinated against Covid, and is the chair of the National Space Council.”

Sometimes, it’s better to say less.

Harris’s defenders note — fairly, I think — that, as a Black woman, she is held to a different standard. But we’ve also seen plenty of men in national politics who burst onto the scene with a kind of celebrity only to reveal themselves, in time, as lacking discernible depth. (John Edwards and Marco Rubio come to mind.) Harris’s problem is that, like them, she seems to view politics as a series of theatrical opportunities.

This was clear early in her calamitous presidential campaign, when she earned a huge debate moment by attacking Biden over his stance on forced busing in the 1970s. Pressed to elaborate later, Harris couldn’t point to any substantive difference with Biden on desegregation. The performance quickly faded from memory, and Harris’s campaign flailed. She ran out of money and withdrew before any votes were cast.

That Democratic leaders did nothing to dissuade Biden from seeking a second term is, itself, a testament to how much Harris worries them. A lot of Democrats will tell you that, while they had doubts about renominating a man Biden’s age, they could see no one other than Harris who might take his place — a prospect sufficiently ominous as to unify the party.

There’s been talk of replacing Harris on the ticket (as there is with most vice presidents at one time or another). The former White House counsel Greg Craig even argued that Biden should throw the choice of a running mate open to the Democratic convention, as FDR once did. It’s not going to happen, and shouldn’t. So what does Biden do?

His inclination, I’m guessing, will be to deploy Harris strategically, relying on her to rally women and Black voters over abortion and voting rights. This is what vice presidents normally do, after all, and given what’s been happening in courts and state legislatures, it would seem like an obvious assignment for a running mate who can speak personally to issues that galvanize the Democratic base.

In this case, however, the usual strategy might be exactly the wrong one. Because much as they want to believe otherwise, candidates and parties don’t get to decide what a campaign is really about — voters do. And if voters believe they’re being asked to elect not just a president but possibly the next president after that, then there’s really no getting around the issue.

Biden can talk all he wants about how vigorous he is, and his consultants can show him biking or jogging or wrestling a grizzly bear. But in the end, Americans will see and hear a president who would be 86 by the time he completes a second term. They have a right — if not an obligation — to factor in his potential replacement (just as they should if Trump, now 76, is again the Republican nominee).

So if I were giving Biden advice he surely doesn’t want, I’d tell him to steer into the storm rather than away from it, and run with Harris almost as if he expected her to take over. I’d make her a constant fixture at Biden’s side in public events and in the kind of extended interviews she’s mostly avoided doing. I’d turn the campaign into what Hollywood calls a “two-hander” — a show with two protagonists.

Because this is the lot Biden chose, inevitably, when he elevated Harris nearly three years ago. He knew the stakes. He must have believed then that she had the ability to win over voters and lead the nation if it came to that — and it’s hard to believe she could have come this far if she didn’t. There’s really no choice now but to find out.