With the formal launch of 80-year-old President Biden’s re-election campaign via a video announcement, Americans should be preparing for the real possibility of a President Kamala Harris.

Mr. Biden is now the oldest president to serve in office. If he wins re-election in 2024, he will be 86 years old at the end of his second term. 

People show signs of aging — both physically and mentally — at different rates. Yet what many a person with an octogenarian family member will tell you is that the rate of decline increases precipitously after 80. Mr. Biden has already surpassed the median life expectancy of American men. For the top 1 percent of income earners, life expectancy jumps to 87 years of age. That’s still cutting it close.

“People are living longer. He’s in good physical shape,” a Democratic strategist, Hank Sheinkopf, tells the Sun. Yet he warns, “Should people be prepared for Vice President Kamala Harris? The man is 80 years old. People should be prepared for change.”

Eight presidents have died while in office, four of them from natural causes and four from assassinations. While it hasn’t happened since President Kennedy was killed in 1963, there is a reason we have vice presidents.

There’s also the less morbid scenario of a potentate choosing to retire early due to infirmities. That’s what Pope Benedict did when he abdicated in 2013 at age 85.

The White House press secretary, Karine Jean-Pierre, fueled speculation about this scenario when she refused to say on Tuesday that Mr. Biden would serve a full term if he wins re-election. “That’s for him to decide,” she told reporters. She later clarified via Twitter that Mr. Biden would do so.

Concern over Mr. Biden’s age is not just a right wing obsession. The New York Times recently ran an editorial imploring Mr. Biden to talk about his health and mental acuity with the American people and to reassure voters that he is fit to serve. “Concerns about age — both in terms of fitness for office and being out of touch with the moment — are legitimate,” the Times wrote.

Nearly 70 percent of registered voters say Mr. Biden is “too old for another term,” according to a February Yahoo News/YouGov poll. More Democrats — 48 percent — agree with that statement than the 34 percent who disagree. President Trump is only four years younger than Mr. Biden, though this same poll found that fewer Americans (45 percent) think Mr. Trump is “too old for another term.”

Mr. Biden’s reticence to talk to reporters or hold press conferences, his stumbling on the stairs leading up to Air Force One, and his gaffes are fueling speculation that he is slowing down. The Democratic National Committee will not be holding primary debates, even though Mr. Biden does have two long-shot challengers. With the campaign launch being done via a pre-recorded, highly produced video, there is speculation Mr. Biden will be repeating his basement campaign strategy of 2020. It worked once.

“It’ll be very interesting to watch how the Biden campaign conserves him and conserves his energy in terms of campaigning,” a political science professor at the University of New Hampshire, Dante Scala, tells the Sun. “How much of the Biden strategy in ’24 will be a Rose Garden strategy?”

Mr. Sheinkopf says not holding debates is probably a smart move. “Incumbents tend to make errors,” he says, pointing to President George H.W. Bush and the “read my lips” comment that backfired. He says the age issue will be more important if Republicans nominate a substantially younger candidate than Mr. Biden — not Mr. Trump. Mr. Scala counters that Mr. Biden could emulate President Reagan with his own “youth and inexperience” quip.

In a preview of how Mr. Trump will handle the topic of age if he wins the Republican nomination, he refused in a Fox News interview last month to say whether Mr. Biden is in cognitive decline. “I don’t want to say that. I don’t think it’s appropriate for me. You can say it,” Mr. Trump said to Sean Hannity. 

(This showed uncharacteristic restraint for Mr. Trump, who’s spent years accusing “Sleepy Joe Biden” of intellectual deficiencies, including that he “has dementia.”)

Mr. Sheinkopf says Mr. Biden’s age will mean “even greater scrutiny of [Ms. Harris’s] behavior, her comments, her foreign policy, and on domestic issues.” It will likely make Mr. Trump’s vice presidential pick more important as well.

“If it’s Trump, we’re having the same conversation,” Mr. Scala says.

Ms. Harris has struggled to define her role in the White House. She has been plagued by low approval ratings since she was tasked with solving the crisis at the southern border amid a surge of crossings in 2021. Since then, her approval rating has recovered slightly, though it still hovers at 40 percent. She recently hired a new senior advisor to focus on messaging.

Ms. Harris did earn praise for a speech she gave this month at Nashville to support the “Tennessee Three,” lawmakers who faced expulsion after joining a protest for gun control and using a bullhorn on the house floor. 

Her bumbling speeches and comments elsewhere, though, have earned her the mockery even of Comedy Central’s “The Daily Show,” a left-leaning program by any measure. It aired a video compilation of Ms. Harris’s speeches cut with the fictional, inarticulate vice president on HBO’s political satire show, “Veep,” to show the cringeworthy similarities.

Ms. Harris has also been dogged by reports of turmoil and unnaturally high turnover rates among her staff. Her personnel issues go back to the days of her ill-run presidential campaign. 

Ms. Harris does have her supporters, including on “The View,” who have said that Ms. Harris is facing more scrutiny because she is a woman and Black. “I don’t know if that’s true,” Mr. Sheinkopf says. “Dan Quayle got a lot of bad publicity because he was not the brightest bulb.”

In January, Senator Warren’s ambivalence toward the vice president on a Boston Public Radio program fueled speculation that Mr. Biden might choose another running mate for 2024. “I really want to defer to what makes Biden comfortable on his team,” Ms. Warren said, when asked about Ms. Harris being part of the ticket. Ms. Harris was said to be so enraged she refused to take a call from Mr. Warren, who was quickly trying to clean up her mistake.

So should President Biden just cut his losses now and drop Ms. Harris unceremoniously from the ticket?

“He cannot drop a Black woman and expect to be successful in a contested race,” Mr. Sheinkopf says. “He needs every Black vote to turn out that he can get his hands on.”

Mr. Biden’s announcement makes clear that Ms. Harris will indeed be on the ticket. In 2024, the bottom of the ticket may be as important as the top.