Early on in Thursday’s Democratic presidential debate, Eric Swalwell, the 38-year-old U.S. congressman from California, decided to take his shot at Joe Biden. He recalled how, when he was just 6 years old, a politician had come to the California Democratic Convention and said it was time to “pass the torch to a new generation of Americans.”

“That candidate was then-Sen. Joe Biden,” Swalwell said, delivering the punchline to a mix of groans and applause. “Biden was right when he said it was time to pass the torch to a new generation of Americans 32 years ago. He’s still right today.” Biden, the front-runner heading into the debate, smiled broadly, taking the dig in stride. “I’m still holding onto that torch. I want to make that clear to you,” he said in response. Then he started reciting a dry, stumbly bit about education policy. It was hard to follow.

In that moment, the whole depressing subtext of the former vice president’s campaign temporarily became text. Biden is old. At 76, he would be the most-senior first-term president in history. But unlike his fellow septuagenarian, Sen. Bernie Sanders, it was impossible to watch Biden debate without noticing just how many steps he seems to have lost. He’s still gripping onto the torch, yes, and running toward an office he’s desperately wanted since he was a young man. But—and I say this due to his performance not just his birthdate—it’s hard to imagine he has the strength to keep it up.

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Biden used to be quite good on a debate stage. Sure, sometimes he got a little mush-mouthed and tripped over his words, or said something stupid. But even when he couldn’t quite talk straight, he could certainly communicate. He could joke. He could emote. He could evince outrage and modulate back to avuncular Catholic pol mode. His best moment in 2008 was his one-line evisceration of Rudy Giuliani—“There’s only three things he mentions in a sentence: a noun, a verb and 9/11”—but go back and watch his highlight reel, talking about foreign policy or the tragedy that left him a single father. If nothing else, he could convey sincerity.

Thursday night will mostly be remembered for Biden’s confrontation with Sen. Kamala Harris, who deftly attacked him for working with segregationists to oppose school busing in the 1970s and recalled how she herself was bused as a little girl. Biden looked grim, then angry, then stammered through an indignant, difficult-to-parse response:

The fact is that in terms of busing. The busing I never—you would have been able to go to school the same exact way because it was a local decision made by your city council. That’s fine. That’s one of the things I argued for that we should not be—we should be breaking down these lines. So the bottom line here is, look, everything I have done in my career, I ran because of civil rights.

But Biden’s problem wasn’t a single bad moment. It’s that he showed hardly any of the old skills that once made him such a relatable public presence. He didn’t talk to the audience so much as recite—alternately shouting and wobbling through stretches of accomplishments or proposals, during which his grammar and syntax seemed to get increasingly confused as he went along. Take the riff that followed after moderator Chuck Todd suggested his talk of bipartisanship in Washington was outdated. “It does sound as if you haven’t seen what’s been happening in the United States Senate over the last 12 years,” Todd said. To which Biden answered:

I have seen what happened. Just since we were vice president. We needed three votes to pass an $800 billion recovery act that kept us from going into depression. I got three votes changed. We needed to be able to keep the government from shutting down and going bankrupt. I got Mitch McConnell to raise taxes $600 billion by raising the top rate. As recently as, after president—uh—got elected, I was able to put together a coalition of a Cures Act. That billions of dollars go into cancer research. Bipartisan. But sometimes you can’t do that. Sometimes you have to go out and beat them. I went into 20 states, over 60 candidates. And guess what? We beat them.

It’s not the pure logorrhea of a Trump soliloquy. Instead, it’s a guy reaching for his canned response and losing himself as he goes on. You can see the potholes opening up in his sentences as he keeps going.

Again, Biden isn’t the only older candidate in the race. Sanders, at 77, is a year his senior. Trump, at 73, seems deep into some sort of cognitive decline. The difference is that as they’ve gotten older, Sanders and Trump have just become concentrated versions of themselves. Onstage, Sanders is still the angry revolutionary, shouting out stats about inequality and rejecting the moderators’ questions; in interviews, he’s still sharp and often quite funny, in his cranky Jewish grandfather way. You could see his spryness when he all but leapt up to respond to Swalwell’s torch line. “The issue is not generational,” he bellowed. ”The issue is who has the guts to take on Wall Street.” Trump, meanwhile, is pure, Fox News–imbibing id, embodying all the resentments of his base, while providing lowbrow insult comedy on Twitter. Biden, in contrast, is a paler shade of himself. You see the indignation and the trouble with words, but less of the warmth, less of the humor, less of the basic political skill that used to come naturally to him.

Up until now, much of the conversation about Biden’s candidacy has focused on whether his policy record in Washington and views on politics were too out of step with today’s Democratic Party. The question has been whether he’s too old-fashioned, too much of another era. After Thursday’s debate, you have to ask whether he’s just too old, period.