The revolution just got a little more likely. The socialist junior senator from Vermont, Bernie Sanders, who has twice run spirited campaigns for the White House, appears reluctant quite yet to ride off into the Burlington sunset — or snowdrift. 

A memo penned by Mr. Sanders’s 2020 campaign manager, Faiz Shakir, and leaked to the Washington Post informs supporters of the senator that “in the event of an open 2024 Democratic presidential primary, Sen. Sanders has not ruled out another run for president.” 

This admission paints a picture of a potential threat to President Biden emanating not from a younger candidate, but from Mr. Sanders, an even older one. Doubts over Mr. Biden’s future portend a tumultuous next chapter in his party’s, and the nation’s, politics.    

Mr. Sanders himself has said that the chances of him running again are “very, very slim,” and the senator would be 83 on the day a president is inaugurated in January 2024. Nevertheless, it is clearly a possibility for his inner circle.   

The memo instructs those same supporters to answer any questions about the 2024 race with that information “in mind.” A spokesperson for Mr. Sanders reminds readers: “Senator Sanders is the most popular office holder in the country.”

Rumblings of a third presidential run for Mr. Sanders come against the backdrop of plunging presidential poll numbers for Mr. Biden. CNN’s poll of polls puts his approval rating at 39 percent, with a robust 55 percent disapproving. Qunnipiac pegged that president’s approval at a parlous 33 percent.  

That same Quinnipiac survey found Mr. Biden’s approval rating among Hispanic voters at a stunning 26 percent. His grades on the economy continue to deteriorate, as inflation sets prices skyrocketing and views of Mr. Biden tumbling. 

When Americans turn to Mr. Biden’s second-in-command, they are far from impressed. A recent Economist/YouGov poll put Vice President Harris’s approval rating at nine points underwater. A RealClearPolitics average of polls discloses that less than three in 10 Americans believe the country is on the right track. 

Even discounting for Mr. Biden’s age alongside his weakened political position, it is surprising how much speculation is swirling about someone else running on his party’s ticket in 2024. A Wall Street Journal survey found that fewer than half of Americans believe that the president will seek a second term. 

The White House press secretary, Jennifer Psaki, has said that it is Mr. Biden’s “intention” to run again in 2024. The Hill reports that Mr. Biden told President Obama that he will run in 2024, and the president remarked that he would be “very lucky” to have a rematch against President Trump.  

While previous speculation reported by Politico centered on Representative Ro Khanna, a progressive of Silicon Valley and a co-chairman of Mr. Sanders’s 2020 campaign, as a possible 2024 candidate, the possibility of Mr. Sanders himself jumping back in the hunt for the presidency has now come into focus.    

Longtime colleagues in the Senate, Messrs. Sanders and Biden have enjoyed a seemingly cordial rapport despite their ostensible ideological differences. Their competition was not marred by the kind of discord that defined Mr. Sanders’s 2016 run against Hillary Clinton.

That would no doubt change should Mr. Sanders, sensing a vulnerable president and an unlikely opening, grow bolder and seek more overtly the ultimate prize that has twice eluded him.