President Biden’s campaign is circling the wagons around his embattled vice president, Kamala Harris, who is struggling to overcome a 38.7 approval rating amid criticism of her competence and fitness for office. Ms. Harris’ approval rate, gleaned from a FiveThirtyEight average of polls, is even lower than Mr. Biden’s 41.2 percent rating.

According to FiveThirtyEight, Ms. Harris’ disapproval rate averages out to 52.1 percent. Her prospective candidacy is under unusual scrutiny due to Mr. Biden’s advanced age — he will be 82 on Inauguration Day, 2025 — with some Republicans arguing that Mr. Biden’s infirmities mean that a vote for him is a vote for Ms. Harris.

To bolster her candidacy, the White House is putting Ms. Harris out in front of a popular issue among Democrats: abortion rights. On Saturday, Ms. Harris is set to deliver an address at Charlotte, North Carolina, on the anniversary of the Dobbs v. Jackson Women’s Health Organization decision overturning Roe v. Wade. 

The event is aimed at addressing an issue that has become central to the Democratic platform since the decision was handed down and likely helped Democrats in last year’s midterms.

The speech, however, also has a second objective — to give Ms. Harris an opportunity to connect with voters on an issue that is a winner for Democrats.

In recent months Ms. Harris has taken a central position in messaging from the administration and the re-election campaign, especially concerning topics like abortion and infrastructure. During the debt talks, for example, Ms. Harris often sat between Mr. Biden and Speaker McCarthy on camera.

The vice president also featured prominently in the re-election announcement video and has spent the spring traveling to promote the administration’s agenda.

Ms. Harris’ positioning is in part meant to push back on criticism from Republicans about the prospect of Ms. Harris being next in line to the presidency of a man who will be 82 years old on Inauguration Day, 2025. 

Republicans from the New York Post columnist Miranda Devine to Governor Christie have been making the claim that, in the words of Ms. Devine, “A vote for Joe Biden is really a vote for the risky adventure of President Kamala Harris.”

For Republicans, the criticism not only capitalizes on one of Mr. Biden’s most vulnerable characteristics but also on Ms. Harris’ weak approval numbers, even when compared to Mr. Biden.

The former ambassador to the United Nations and Governor of South Carolina, Nikki Haley, took a line of attack that’s becoming typical of Republican presidential hopefuls in a recent interview with Fox News.

“I think we can all be very clear and say with a matter of fact that if you vote for Joe Biden, you really are counting on a President Harris because the idea that he would make it until 86 years old is not something that I think is likely,” Ms. Haley told Fox News.

 Ms. Harris’s lagging approval rating is driven by lower approval ratings among Democrats, according to data provided by YouGov. Among Democrats, Ms. Harris enjoys only a 74 percent approval rating, compared to Mr. Biden’s 89 percent approval.

Among Republicans, the two have identical disapproval ratings of 80 percent each. Among independents, the disapproval rating is also comparable, at about 62 percent for Mr. Biden and 61 percent for Ms. Harris.

The lack of enthusiasm among Democrats about Ms. Harris is why some in the party, like the White House counsel to President Obama, Greg Craig, floated the idea prior to the announcement of a re-election campaign that Mr. Biden should allow the vice presidential candidate to be chosen at the party’s convention like President Roosevelt did in 1944.

“Allowing Democratic voters to pick the vice-presidential nominee might address the Democrats’ enthusiasm gap,” Mr. Craig wrote for the New York Times. “If the status quo continues, no one on the Democratic side will excite or inspire a crowd.”

This, however, didn’t happen, and Republicans have been eager to take advantage of what is shaping up to be an unexciting Democratic ticket.

Mr. Biden has been quick to defend Ms. Harris as his number two, telling MSNBC last month that “I just think that Vice President Harris hasn’t gotten the credit she deserves.”

“She is really very, very good,” Mr. Biden said. “And with everything going on, she hasn’t gotten the attention she deserves.”

Other Democrats have begun to circle the wagons too as the party prepares to back Mr. Biden for re-election in 2024 despite anxiety voters have about his age and health.

“The vice president, like many vice presidents, has struggled to get positive press coverage and to get the credit she deserves for the hard work that she’s been doing,” Congressman Chris Coons, a close ally of the White House, told ABC.

Although Mr. Biden’s age and Ms. Harris’ role as his potential successor have been dominating headlines due to the fact that they are almost universally expected to become the Democratic nominees, Mr. Trump’s vice presidential pick might become a hot topic due to his age as well.