“That man is like superhuman,” Joy Manbeck told The New York Times at the annual People’s Summit in Chicago earlier this month. “He still plays basketball. He walks to work. I don’t care. I want him. Period. I want Bernie.” So does RoseAnn DeMoro, the indefatigable leader of the National Nurses United union. In an interview with McClatchy, she said the Vermont senator is “so clearly ahead” of other potential contenders in the nascent 2020 Democratic presidential field. She added, “He has the most comprehensive program. He’s been doing this his whole life. What people want is what Bernie is saying.”

She has a point. An April Harvard-Harris survey revealed that Sanders is the most popular politician in the country: 80 percent of registered Democrats and 57 percent of voters overall say they approve of him. During the 2016 primary, Sanders won key states that Hillary Clinton later lost to Donald Trump; her defeat was at least partly attributable to an “enthusiasm gap” among expected Democratic voters. Sanders himself has not indicated that he’s planning another White House run, but thanks to his popularity and the unexpected viability of his primary campaign, questions about his political future are being asked.

But all this speculation does prompt another, equally important, question: Should Sanders run? The answer is no, though not for the reasons his critics think.

The imprudence of a Sanders run has nothing to do with his status as an independent. Nor does it have anything to do with the other criticisms his opponents tend to lob in his direction. He did not cost Clinton the election; her loss can be attributed to myriad campaign failures, Russian interference, voter disenfranchisement, and the infamous Comey letter. He is not working at cross purposes with the Democratic Party; he has in fact campaigned for the party’s candidates at its request and in fulfillment of his role as the party’s outreach chair. He and his followers do not represent some existential threat to the party’s identity; any winning Democratic coalition will need their numbers and energy, and as such it should reflect their policy preferences.

Still, there is a strong case for Sanders abstaining from making another presidential run. The first obstacle is obvious: He will be 79 next Inauguration Day. Basketball notwithstanding, advanced age is a vulnerability for any politician. This is particularly true of a politician who inhabits the Oval Office—and this critique applies to Joe Biden and other potential contenders of a certain age.