Back in June, then-candidate Joe Biden wrote an op-ed for USA Today and made — well, not quite a promise, but an acknowledgment of a problem that America has never come close to fixing. “Across the board — from our classrooms to our courtrooms to the president’s Cabinet,” he wrote, “We have to make sure that our leadership and our institutions actually look like America.” Naming Kamala D. Harris as his running mate made this plea for diversity seem more than lip service.

Now, as president-elect, he’ll soon be in a position to address the problem not just at the scale of a presidential ticket but in an entire administration. Court challenges and bad sportsmanship by President Trump and his allies are temporarily logjamming the transition of power, but in the meantime, Biden should make another pledge. He should commit to a Cabinet that is at least 50 percent women.

The shrewd reason: He owes it to them. He owes his large popular-vote margins to women, just as Democratic presidents have owed their margins to women for the better part of three decades. Though 2020 exit polls are still murky and incomplete, early analysis shows Trump won men by eight percentage points; if men were the only voters, the election would look very different. Women voted for Biden by double-digit margins.

The bandwagon reason: Other countries are ahead of the United States on this. Canadian Prime Minister Justin Trudeau committed to gender parity in his Cabinet, as did French President Emmanuel Macron. In the cabinets of Finland, Sweden, South Africa, Costa Rica, Rwanda and Colombia, the numbers of women are equal to or greater than the numbers of men.

The practical reason: It should be easy. Women equal or outpace men in law school, medical school and college undergraduate programs. There have never been more of them in Congress (in this month’s election, 102 Democratic women and 32 Republican women were elected to the House of Representatives). There is no shortage of qualified women, no blockage in the pipeline, no drought in the talent pool.

The real reason: In the Year of our Lord 2020, there is simply no defensible reason not to.

If a president today cannot come up with a qualified Cabinet 50 percent composed of women or nonconforming genders, this reveals something unpalatable about the person in office.

The tired response to these arguments is going to be that Biden shouldn’t be thinking of gender but about “the best person for the job.” It’s a shopworn excuse. When Vice President Pence released a photo of the White House’s early coronavirus task force — the 17 people in it were all men, and nearly all White — the administration’s defenders argued that this was no time to be politically correct; this was the time to find “the best people for the job.”

That explanation only highlighted the problem. The White House presumably had access to the best scientific minds in the country. Given carte blanche to recruit the smartest people, the administration looked as hard as it could and determined that — huh, weird! — all of the smartest people were men. They were telling on themselves.

The story was the same for Donald Trump’s senior appointees at large, among whom there are only four women vs. 19 men in Cabinet or Cabinet-level positions. And for Barack Obama, where the ratio was seven to 16. And for George W. Bush, whose outgoing Cabinet contained only five women.

Every one of these presidents is likely to have thought that he was filling each slot with the most qualified person. What each was actually doing was making clear that his search had been too narrow. All lived in a world in which powerful men worked with and networked with one another, and thus noticed, hired and promoted one another. This might be familiar to some of you who work in other industries. Men form professional bonds with other men, whom they genuinely think are great; in fact, they can’t think of a better fit for whatever job opening crosses their radar. Which is not to say there isn’t someone better.

Gender parity in hiring is a complicated social puzzle with hundreds of antique pieces: old boys’ clubs, women’s under-confidence in job applications, a lopsided division of domestic labor that impacts spouses’ abilities to rise equally in their careers. But a job fair as elite as a president’s Cabinet waiting to be filled is the perfect opportunity to show how it’s done.

If you truly believe that women are as smart and capable as men, you should be hiring them at rates equal to your rates of hiring men. Not because you’re scrambling to fill quotas with lesser candidates, but because that’s the natural outcome of following through on what you say you believe about how talent is distributed in the workforce.

Gender parity reflects thought parity — it’s a window into how candidates view talent and intelligence, and how hard they’ll work to find the actual best people. It’s also a way for the country to glimpse a better version of itself. No woman or girl should have to look at a group photo of the country’s designated brightest minds, and notice that all of them are guys. No man or boy should do that, either.

The early days of the Democratic primaries — when the contest included six women and multiple candidates of color — made chances seem high that America would end up with a revolutionary person in the Oval Office. Instead, we’ll end up with Joe Biden.

But he still can be a revolutionary, if he uses his institutional power to create a more perfect Cabinet, one that “actually looks like America.” Which, if you’re reading this, Mr. President-elect, is 50.8 percent female, according to the most recent census.

Round down if you must. Fifty-fifty is a good place to start.

Monica Hesse is a columnist writing about gender and its impact on society. For more, visit wapo.st/hesse.