Three weeks. That’s all it took to overthrow a president.

Joe Biden’s weekend announcement that he would not accept his party’s nomination for another term followed what will go down in history as the single worst presidential debate performance ever.

Bad enough, in this case, to knock Biden out of a race he had already won — the Democratic primary.

Imagine the Lakers beating the Celtics at Crypto.com Arena, only to do something so bad in the locker room afterward that the NBA said: “Guys, we are awarding the Celtics the win because of just how poorly you behaved. ”

The debate was a miscalculation of epic proportions. Biden’s campaign — trailing at the time but close enough to come back and win — asked for it. They scheduled it. They bragged about it.

Trump said yes and let Biden make all the rules. Many in the media crowed that Biden had bested Trump in setting the contours and the expectations.

And then Biden fell on his face.

What followed has been truly stunning. Three weeks of Democrats melting down, Biden defiantly telling them to pound sand and then finally the president bending the knee in a mysterious letter posted during a weekend bout with COVID.

It was plumb weird that the White House didn’t release a photo of Biden this weekend signing the letter or meeting with his political advisors. For the most powerful person in the world to announce an Earth-shattering decision via social media without really giving a reason (reread his letter — you won’t find one in there) just adds to the humiliation for a man who had once said that only the Lord Almighty could drive him from the race.

If he’s dropping out for health reasons, Americans need to know that right now. Because it does call into question his fitness to lead the country presently.

Perhaps the Lord Almighty for Democrats is House Speaker Emerita Nancy Pelosi, who, working with former President Obama and other party leaders, not to mention George Clooney and party donors, mounted the pressure campaign to remove Biden from the race.

Thou shalt have no other speakers before me, I reckon. Read this passage from Politico’s reporting about what happened this weekend:

“ ‘Nancy made clear that they could do this the easy way or the hard way,’ said one Democrat familiar with private conversations who was granted anonymity to speak candidly. ‘She gave them three weeks of the easy way. It was about to be the hard way.’ ”

What was the “hard way,” exactly? Apparently, going public with her advice. Why not invoking the 25th Amendment?

President “Democracy Is on the Ballot” Biden found his end in the most undemocratic way possible — not at the hands of voters, but rather of the political elites.

I was wrong when I predicted that Biden would hang on. I guess I shouldn’t have taken Democrats literally when they said we always must respect the outcome of elections. When you hear that demand this fall, be sure to read the fine print: not applicable to Democratic primaries or when Nancy Pelosi says so.

I was right, though, that the Democrats would turn to Vice President Kamala Harris as Biden’s replacement. Though Harris piously proclaims she wants to “earn” the nomination, anyone can see that the fix is in.

Biden was taken out in an undemocratic way, and Harris will be installed through a rigged process. Inspiring.

For Donald Trump’s part, he simply needs to transfer the arguments he was making against Biden to Harris. She is, after all, just as responsible for Biden’s failures as he is and carries an approval rating in the high 30s, same as the president.

Specifically, I expect the Republicans to laser focus the immigration crisis as the most pronounced of Harris’ failings. Biden appointed her his de facto border czar in 2021, and the situation has only gotten worse since.

Trump was already arguing that a vote for Biden was actually a vote for Harris, as nobody expected Biden to complete a second term. Trump was proven right, albeit on an accelerated timeline.

Democrats are using the talking point that Trump is now the oldest presidential candidate in American history. But they are missing the point — Biden’s numeric age was never the problem. It was his rapid decline and the signs of a cover-up that had Republicans — and most Americans — exercised about Biden’s fitness for office.

Republican Nikki Haley, who lost to Trump in the GOP primary but endorsed him at last week’s Republican Party convention, said in January, “The first party to retire its 80-year-old candidate is going to be the one who wins this election.”

Now the 2024 election will test her theory. Harris, who is 59, will be portrayed in the media as young and vigorous; Trump, old and past tense.

Trump starts ahead of Harris in the national polls. But for the next three weeks, it’s likely that Harris will receive glowing profile after profile, followed by a coronation at the Democratic National Convention.

Trump must step up the pressure and invade her political space as much as possible during this time, proving his own vigor while defining his new opponent as more extreme and incompetent than his former one. His campaign, I have no doubt, is ready to unleash just such an attack.

The question is: Will Americans hold Biden’s record against Harris? Or is simply putting a younger face on a failed administration enough to give it a second chance?

Scott Jennings is a contributing writer to Opinion, a former special assistant to President George W. Bush and a senior CNN political commentator. @ScottJenningsKY