Many Americans view Donald Trump as a uniquely dangerous president, so there is an implicit obligation for Democrats to nominate someone who can beat him.

Beating Trump will require a candidate who has the energy and toughness to take on a world-class virtuoso at Twitter trolling, hurling off-the-cuff comebacks and insults, and discovering and exposing his opponents’ weaknesses.

If you saw Joe Biden’s shaky first debate and then watched Robert Mueller’s halting testimony last week, the idea of pinning your hopes on an aging Trump rival who has lost a step feels increasingly dicey.

The stakes couldn’t be higher for Biden’s next debate performance Wednesday night, when he’ll share the stage with Kamala Harris and Cory Booker, among others.

Take, for example, this from MSNBC political commentator (and noted Never Trump conservative) Charlie Sykes. “I think there’s going to be extra pressure on Grandpa Joe who’s—what, he’s about 106, right?—to see whether he’s going to have senior moments,” Sykes during a recent episode of The Bulwark podcast. “That may be more important than the specifics of what [Biden] says.”

It’s easy to dismiss this politically incorrect take as ageist. But it is a bad political analysis? It might not be fair or right that we prioritize quick wits and bon mots over attributes like experience, but this is the world in which we live. Flaws and all.

And let’s not pretend this is purely a superficial concern about “optics.” Everyone remembers Ronald Reagan’s comeback to the “age” question in the famous 1984 debate. But few people remember the moderator’s question: “You already are the oldest president in history, and some of your staff say you were tired after your most recent encounter with [Walter] Mondale,” the moderator said. “I recall, yes, that President [John F.] Kennedy, who had to go for days on end with very little sleep during the Cuba missile crisis. Is there any doubt in your mind that you would be able to function in such circumstances?”

This was relevant, partly because (as the moderator mentioned) Reagan, then 73, had delivered what many considered to be an “uninspired” debate performance—but it was also a legitimate national security question.

But Reagan was ready for it, answering: “ I will not make age an issue of this campaign. I am not going to exploit, for political purposes, my opponent's youth and inexperience.” Reagan’s humorous line put an end to the age question.

Having delivered his own uninspired debate performance last month, Biden has likewise invited questions about whether he’s sharp enough to take on Donald Trump in 2020—and whether he’s up to the challenges of governing.

Like Reagan, Biden has an opportunity to bury the age issue, once and for all, by demonstrating energy and intellectual vigor. Is Joe Biden going to come out of Motown riding high, or looking like he got run over by a Ford truck? Is he Robert Mueller or Ronald Reagan?

This is his opportunity to answer those questions.

The good news for Biden is that a lot of Americans are rooting for his success.

There has never been a better time to be an old presidential candidate. Consider that Biden, 76, is running against Bernie Sanders, 77, for the chance to take on Donald Trump, 73. (They are all babies compared to Supreme Court Justice Ruth Bader Ginsburg, 86, who takes special glee in outliving her critics.)

This system is enabled by a cable news viewership, an electorate, and a donor class that skews decidedly geriatric.

As Pew recently noted, “In 2020, nearly a quarter of the electorate (23%) will be ages 65 and older, the highest such share since at least 1970.” Older people are also more likely to make a campaign contribution.

“ Is Biden too old and tired to beat Trump? That is the biggest question in America right now ”

What is more, according to Pew, “ The average donation rate for those ages 18 to 29 is 9%, compared with 12% for those 30 to 49, 14% for those 50 to 64, and 32% for those 65 and older.”

Voters, viewers, and donors who themselves are in their sixties might be more inclined to engage in some wishful projection. They probably don’t want to admit that Biden is past his prime any more than I want to see Tom Brady take his last snap.

This is his chance to prove he can still quarterback his party.

Is Biden too old and tired to beat Trump? That is the biggest question in America right now—and it is one on which we might soon reach a consensus.

A lot hinges on which Joe Biden shows up in Detroit on Wednesday. The main thing he needs to do here is to avoid anything that would confirm the looming narrative. Biden doesn’t necessarily need a funny retort, or even a dominating performance. What he does need to do is to avoid losing his train of thought or being caught flatfooted with a vacant look in his eyes.

He just needs to deliver a performance that doesn't raise questions about whether he can handle the rigors of a campaign . The way to defeat this meme is to starve it.