Is President Xi Jinping having trouble letting go of power? Apparently unscripted comments caught on a hot microphone at Beijing find Mr. Xi fretting about longevity. Mr. Xi, 72, was heard musing to President Vladimir Putin that “earlier, people rarely lived to 70, but these days at 70 years you are still a child.” Mr. Xi reckons “there’s a chance of also living to 150.” It could, one imagines, prove a longer than expected tenure for China’s party boss.

Mr. Xi’s remarks underscore one of the critical distinctions between a self-governing nation and a communist regime such as China. In a free nation, the rulers are public servants with legally limited terms of office. Messrs. Xi and Putin have both extended indefinitely their terms in power. This open-ended tenure is a hallmark of undemocratic rule — and of their apparent reluctance, or outright refusal, to cede power voluntarily. 

If Mr. Xi appears to envision ruling China into the 22nd century, Mr. Putin’s reply suggests he’s thinking on an even longer scale of time. “With the development of biotechnology,” Mr. Putin said, “human organs can be continuously transplanted, and people can live younger and younger, and even achieve immortality.” When people used to cheer “Long Live the King,” one imagines, this is not what they had in mind. 

Mr. Putin’s reflections about defying death prompted Mr. Xi’s more measured suggestion that “predictions are, this century,” of lives spanning some 15 decades. With that, the audio of this apparently spontaneous conversation was cut off. Yet the insight to be gleaned from this exchange is no less remarkable for its brevity. Are such intimations of immortality what beguile the men who preside over the world’s two leading authoritarian superpowers? 

To be sure, Mr. Xi has been at pains to remain atop the communist regime at Beijing. “For more than a decade,” Tyler Jost and Daniel Mattingly report in Foreign Affairs, “Chinese politics has been defined by one man,” and the nation faces the prospect of “years, perhaps even more than a decade, before he steps down.” Even so, Messrs. Jost and Mattingly predict China’s next few years are going to be “defined by the question of succession.”

Yet Mr. Xi has already broken a guardrail of sorts in Chinese politics by extending his reign as party boss into a third term. That limit — however faint an echo to Washington’s restraint in forgoing a third term — was imposed by China’s communists in the aftermath of Mao’s disastrous open-ended despotism. Bloomberg reports that Mr. Xi, having “ended presidential term limits,” could be “set for a potential fourth term leading China in 2027.”

Mr. Xi’s musings on life expectancy, though, could reflect fears over his legacy. A “vacuum” left after the rule of “a strongman such as Xi,” Messrs. Jost and Mattingly write, could spark “a scramble for power and a fight over the direction of the country,” but also open the door for a “more moderate and temperate leader” to take power. That would repeat the rise of a reformer like Deng Xiaoping within a few years of Mao’s death, Messrs. Jost and Mattingly aver. 

Messrs. Xi and Putin’s qualms over death suggest, too, a contrast with the old model of Western monarchy that saw even kings as subject to the higher authority of God. This was marked when Charles was anointed at his coronation. The sentiment behind Psalm 39, after all, is antithetical to the egotism of dictators like Messrs. Xi and Putin: “Lord, make me to know mine end, and the measure of my days, what it is; that I may know how frail I am.”