President Biden on Sunday did something unusual for a president, Democratic or Republican: He explicitly endorsed the right of workers to organize into unions.

The prompt for the message released by the White House was an organizing drive for Amazon workers in Alabama. (Amazon founder Jeff Bezos also owns The Washington Post.) Biden didn’t encourage the workers to vote to join the union, mind you, but he did offer his support for the right of those workers to have that choice.

This isn’t typical presidential behavior, even for a Democrat. When Biden was vice president, President Barack Obama had an often rocky relationship with organized labor. Former president Bill Clinton used opposition to unions as a way to broaden his base of support. Donald Trump and George W. Bush, of course, were never expected to express anything but hostility to labor.

But particularly for Biden, and particularly in this moment, his approach makes sense.

1. Union members earn higher wages.

The most immediately obvious reason is that union members (and those represented by unions but who don’t pay dues) earn higher wages than other workers. Overall, union members in 2020 had median earnings 15 percent higher than nonunion workers, according to the Bureau of Labor Statistics. Among White union members, earnings were 19 percent higher; among Black and Hispanic workers, union members made 26 and 39 percent more, respectively.

(The overall figure is for workers ages 25 and older. For racial and ethnic groups, the numbers are for those 16 and older.)

There is an important qualifier to those numbers. The massive job losses that followed the implementation of efforts to contain the coronavirus last year meant that many lower-paid workers lost their jobs, including in more heavily unionized industries like hospitality. But the same pattern held before the pandemic. In the five-year period from 2015 to 2019, union members overall had average earnings 19 percent higher than nonunion employees.

2. Higher wages lower the bar for expanding union membership and raising the minimum wage.

It’s important to also recognize the broader political context of the moment.

One of the reasons that activists and elected officials support expanding union membership is that higher wages in one place make it easier to raise wages elsewhere. Imagine a city with three businesses in the same industry, all of which pay $8 an hour. If Company A’s workers unionize and push their wages up to $12 an hour, it puts pressure on Companies B and C to do the same to attract workers. (This is assuming that the increased wages don’t significantly damage the company’s bottom line, of course, which is the obvious flip side to the argument.) It similarly makes it easier to organize Company B or Company C, both because workers see the benefits of joining a union and because the companies face less of a competitive disadvantage in paying higher wages.

That latter point holds more broadly, too. A region in which few employers pay more than $8 an hour is a region in which a $15-an-hour minimum wage is seen as prohibitive. But if half of the workers in that region are already making $15 an hour, a universal increase of the minimum wage to that level would necessarily cause less friction.

If workers across the United States vote to join unions and see pay and benefits improve as a result, it becomes politically easier to raise the minimum wage nationally — a stated goal of the Biden administration.

3. Unions are important communications vehicles for Democrats.

There’s long been an alliance between labor and the Democratic Party. That alliance trades Democratic support for organizing and strong union contracts (particularly in government) with union backing for Democratic candidates.

That backing includes actual efforts to communicate endorsements to union members. This is enormously useful for Democrats as a turnout mechanism: While the party can and does send mail to voters or run television spots, unions can and do tell workers about endorsed candidates at the workplace. The “organized” part of “organized labor” means that the workers can act with one voice in negotiations with employers but also that they can hear from union leadership more immediately and forcefully than your average Democrat.

4. The Democratic base is more heavily unionized.

Union members tend to vote more Democratic than other Americans, both because of internal messaging and because of shared economic interests. (Exit polling suggests Biden won union members by 16 points in 2020 while tying among nonunion members.)

But it’s also the case that Black Americans in particular are more likely to be union members than other racial or ethnic groups. (The 2020 jumps below are again likely related to job losses from the pandemic — the number of union workers fell, but by a smaller percentage than the number of workers overall.)

In the message posted Sunday, Biden refers to how unions “lift up workers, both union and nonunion, but especially Black and brown workers.” BLS data support that claim.

5. Biden’s pitch has always incorporated working-class Whites.

But of course, Biden’s success in 2020 was also predicated on his relative support from working-class White voters. The Democratic Party has been losing support from this group for decades. In 2016, Hillary Clinton lost non-college-educated Whites by 37 points, according to exit polls, about the same margin by which Biden lost that group. But while Biden won union households by 16 points, Clinton won them by only 5 percent.

In 2020, exit polling suggests that White members of union households split their support between Trump and Biden. Four years earlier, Clinton lost those voters by 12 points.

There’s a common complaint among rank-and-file union members that the movement’s loyalty to Democratic officials hasn’t been reciprocated. Shortly before the 2020 election, I spoke with former classmates of mine who still lived in the area of Northeast Ohio where we went to high school. I wanted to hear from them why they thought the region was shifting so hard to the right.

“I feel like the Democrats are such hard believers in the unions and the unions, I think, failed a lot of Democrats,” one former classmate told me. “So I think — I think that is what has caused the turning to the Republican Party in this area.”

While the union drive at Amazon in Alabama is among employees who are heavily non-White, Biden is also sending a signal more broadly to union members that he will advocate for their right to organize. He’s sending a signal, if you will, that he will try not to fail them as his predecessors had.

None of this is as simple as the above delineation suggests. But there are a number of good reasons, including potent political ones, for Biden to have taken the position that he did.

Emily Guskin contributed to this report.