By the time the presidential debate was over, President Biden looked like some athlete in a contact sport who waited too long to retire. Slack-jawed, hoarse, dazed, gazing vacantly into space, desperately trying to complete a thought, a sentence, or distinguish between billions, millions, or trillions, Mr. Biden looked like he was barely going to make it safely to bed tonight, let alone to the end of his presidency. Asking America to trust him to lead the country for another four years seemed preposterous.

The poor performance leaves the Democrats with a dilemma. Mr.  Biden did terribly, but maybe not quite so terribly that it justifies swapping him out at this juncture for another candidate. The other potential candidates all poll worse or the same against Mr. Trump. Leapfrogging a white man or white woman — Governor Shapiro, Governor Newsom, Gretchen Whitmer, Gina Raimondo — to the top of the ticket ahead of Vice President Harris might leave the Democrats in no better shape. 

If Barack Obama, Jill Biden, and Ron Klain went together to Mr. Biden, showed him a supercut highlight reel of debate lowlights, and suggested he retire for the sake of the country, Mr. Biden might listen. Yet the problem with that scenario is that there’s just no obvious strong winning replacement candidate standing on the sidelines. That’s Mr. Biden’s fault for making the poor choice of Ms. Harris as a vice president.

The Democrats’ best remaining hope is that voters will respond better to Mr. Biden’s sunny view than to Mr. Trump’s dark description. The two candidates offered starkly contrasting assessments of America’s stature.

“We’re a failing nation right now,” Mr. Trump said. “We’re living in hell.”

“We’re the envy of the world. We’re the strongest country in the world,” Mr. Biden insisted.

The questions from CNN’s team of Jake Tapper and Dana Bash tended to back Trump’s assessment, focusing on the inflation that Mr. Tapper said had increased grocery costs to $120 from $100, and what Mr. Tapper called an immigration “crisis.” Mr. Trump had spoken of “Fake Tapper” and speculated that he’d be debating the two moderators along with Biden in a three to one battle, but the CNN team wound up subtly buttressing Trump’s assessment of reality.

Mr. Biden made a few sharp points against Mr. Trump. When Mr. Trump praised turning abortion law back to the states, Mr. Biden said it was “like saying you’re gonna turn Civil Rights back to the states.” When Mr. Trump said America was distanced from Russia and Ukraine by an ocean, Mr. Biden replied that Mr. Putin would head for Poland next and warned, “No major war in Europe has ever been confined just to Europe.”

Often though, Mr. Biden spoke in Beltway jargon — “the A.C.A.” instead of the Affordable Care Act, “Article Five” for the NATO defense obligation. When Mr. Biden attacked in terms voters might easily understand, accusing Mr. Trump of “having sex with a porn star while your wife was pregnant,” the effect was blunted. Instead of being shocked by Mr. Trump “having sex with a porn star,” the shocking thing was that Mr. Biden was awake and well enough to deliver the line without losing his train of thought midway through. Trump responded by denying the sex claim.

On the substance, the two candidates blamed each other for inflation and accused each other of menacing Social Security and Medicare. Mr. Biden criticized Mr. Trump for planned tariffs that he said would raise prices for Americans by $2,500 a year and attacked Trump for tax cuts that “benefited the very wealthy.” Trump said the tax cuts fueled economic growth. “When we cut taxes, we did more business,” Mr. Trump said, sounding like John F. Kennedy, or Arthur Laffer, or Ronald Reagan, or Andrew Mellon.

No one will wind up remembering all that much about the immigration, inflation, tax, abortion or foreign policy parts of this debate, though. They’ll remember Mr. Biden’s near seizures and brain freezes. He’s stuttered since his youth, but the performance he turned in at age 81 was something voters haven’t really seen anything like. Mr. Trump responded at one point, “I really don’t know what he said at the end of that sentence. I don’t think he knows what he said, either.” 

Mr. Biden couldn’t rebut it. His team will have to cancel the second debate and somehow convince the public, perhaps by putting Mr. Biden out with a teleprompter the way he performed at the State of the Union, that the Democratic candidate is still functioning. Anyway, buy oil stocks, sell your shares in electric car manufacturers, and start planning for another Trump administration, because time has caught up with President Biden. 

One feels sorry for the guy. One can inject all the Botox one wants, do all the debate prep, even be right on some of the policy issues. Mr. Biden might be able to defeat Donald Trump, but he can’t defeat time. Even Tom Brady eventually had to retire. It’s not politics, it’s just human frailty, the march of time, and the inexorable process of aging.