Biden did his part. Now here’s the next step.

The idea of an “open process” or a “contested convention” in which Harris competes against other contenders to win the nomination sounds like something Hollywood might script, but I don’t see how that happens in the real world. Convention delegates will have to vote, of course, and other names might be proposed. But I believe the odds of anyone else being the nominee are somewhere between astronomical and ain’t-gonna-happen.

For one thing, all but a handful of those nearly 4,000 delegates are pledged to Biden — or were, until he dropped out. They enter this uncharted political wilderness as Biden people. The fact that Biden immediately gave Harris his full backing will surely be a North Star for many seeking guidance.

I know that some Democrats believe there are other potential candidates who could do better against Trump: Michigan Gov. Gretchen Whitmer, for example, or Pennsylvania Gov. Josh Shapiro, or Kentucky Gov. Andy Beshear. But I disagree. None of the others being mentioned has fought and won a national campaign. None has been subjected to the X-Ray-level vetting that Harris has endured.

And why would any of those rising stars even run? What would they gain by putting themselves out there now, not a month before the convention, in opposition to such power brokers as Bill and Hillary Clinton, who have already called for party unity behind Harris? They have promising futures to think about.

Finally, look at the Democratic Party’s base — the voters who have to turn out in November if Democrats are to beat Trump, hold the Senate and win the House. Members of the Congressional Black Caucus have been among the most ardent advocates of Biden staying in the race. They have made it clear that if the president did withdraw, they and their constituents would have no patience with an effort by the party to “pass over” the first African American vice president in favor of some untested White governor.

No Democrat can win the three “blue wall” swing states — Wisconsin, Michigan and Pennsylvania — without racking up huge vote margins in the Milwaukee, Detroit, Philadelphia and Pittsburgh metropolitan areas. If Black voters stay home on Election Day, Democrats lose.

It is true that Democrats were given a chance to choose Harris in the 2020 cycle, and she didn’t even make it to the Iowa caucuses. But that was then. This year, she has been the Biden-Harris campaign’s most powerful and effective voice on such key issues as abortion and gun safety.

Not incidentally, Harris is by far the most qualified Democrat to serve as president. The vice presidency is often compared to the federal witness protection program, in that it requires self-effacement and blending into the scenery. But she has spent the past 3½ years soaking up a first-class education in foreign policy and sharpening her command of domestic issues.

“Democrats — it’s time to come together and beat Trump,” Biden said in announcing his withdrawal and endorsement of Harris. “Let’s do this.” That should be the spirit that animates Democrats between now and November. Fourteen million voters chose Biden as their presidential nominee, but in voting for the Biden-Harris ticket, they were choosing Harris, too.

For weeks, the party has been in lost a miasma of gloom at the prospect that Trump could win and the GOP could end up with control of both chambers of Congress. Now, Democrats can dispel the fog between their ears and chart a new path. If Harris, 59, is nominated, she will be running against a felon and would-be strongman who at 78 would be the oldest person ever elected president. In what universe is that not a winnable race?

The Democratic convention should be a celebration — of Biden’s generous and historic service to his country, and of the bright prospects of the party’s nominee. It’s a new ballgame.

What do you think President Biden should do with the rest of his time in office? Share your responses with us, and they may be published in The Post.