ATLANTA — Former President Barack Obama’s bid to bolster turnout for Vice President Kamala Harris is falling flat with some Black voters, and Marcus Jean-Francois is one of them.

The Haitian American, who arrived in the United States more than two decades ago, voted twice for Mr. Obama. This year, he is supporting Mr. Trump. He blames Mr. Obama and the Biden-Harris administration for increased crime and rising prices. The Powder Springs, Georgia, resident said life was better when Mr. Trump was president.

“Obama’s policies were so bad for the African American community. Now, inflation is over the top. Things need to change, and we want that change,” he said. “Trump is strong, and we know the former president is going to be different.”

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Mr. Obama is barnstorming battleground states in the closing days of the presidential race to try to increase turnout among the party’s traditionally loyal Black voter base.

This year is much different from Mr. Obama’s historic run in 2008, when Black voters turned out in record numbers and 93% voted for him. Polls show a double-digit drop among Black Americans planning to vote for Ms. Harris compared ​with their support for President Biden in 2020, even though victory would make her the first Black female president.

Mr. Obama has jumped onto the campaign trail to help Ms. Harris. After essentially staying out of the public eye since leaving office in 2017, he can’t rally the Black vote the way he once could.

The former president’s pitch for Ms. Harris also fell flat with Dwayne Prescott, 22, who said he is undecided about how he will vote.

“I was a kid when he was president,” said Mr. Prescott, a drugstore clerk who lives in Macon, Georgia. “I remember nothing that man did besides Obamacare, and that barely did anything.”

He is unsure whether to vote for Mr. Trump but recalls him making life better for the Black community. “I’m not going to say 100%, but I do know for a fact that Trump did help us out.”

Like Mr. Prescott, many young Black voters have little to no memory of Mr. Obama’s presidency. They can recall Mr. Trump’s White House term as a favorable time, with record-low Black unemployment, federal support for historically Black colleges and universities, reduced crime and taxes, and his signing of the criminal justice reform law.

Although Mr. Trump is a billionaire businessman, some Black voters see Mr. Obama, a multimillionaire who owns three mansions and hobnobs with the ultrarich and Hollywood celebrities, as more of an elitist. These voters, particularly Black men, say they aren’t swayed by Mr. Obama and resented his admonishment this month of “the brothers” for refusing to unite behind Ms. Harris.

“People are slowly pushing away the identity of skin color, especially in leadership roles,” said Bruce LaVell, an Atlanta-based senior Trump campaign surrogate who directed the Trump 2016 campaign’s National Diversity Coalition. “That is why the Democratic Party knows that the base is threatened. A lot of those folks in Black culture are getting away from identity politics and want someone to just go and do the damn job.”

Polls indicate Mr. Trump could win double-digit support from Black voters and capture the largest percentage of any Republican presidential candidate since Richard Nixon in 1960.

Nearly 19 million Black voters cast ballots in the 2020 presidential election, according to census data, and they are expected to make up 14% of the electorate this year.

A shift of a few percentage points toward Mr. Trump could easily tip what is expected to be a close outcome.

An October poll conducted by The New York Times and Siena College found that 15% of Black voters, including 20% of Black men, planned to support Mr. Trump, which is more than double what Mr. Trump earned among Black voters in 2020, according to one exit poll.

Mr. Trump’s support increased among younger male voters, according to a GenForward poll released Wednesday by the University of Chicago. The poll found that 26% of Black male voters ages 18 to 40 planned to vote for Mr. Trump.

In Georgia, one of seven critical swing states, Black Americans make up 30% of active voters and are poised to decide whether Mr. Trump or Ms. Harris wins the state. Mr. Biden won Georgia in 2020 by fewer than 12,000 votes.

Nathaniel Duncan, 55, who lives near Macon, voted for Mr. Obama twice. Although one of his younger cousins gravitates toward Mr. Trump, he supports Ms. Harris. He said Mr. Obama remains influential among Black voters.

“I think he makes a difference,” Mr. Duncan said.

Mr. Obama and Ms. Harris will make their first joint campaign appearance in Atlanta on Thursday. Rock legend Bruce Springsteen will join them on stage. Mr. Obama held a rally in Detroit on Wednesday to energize the party base for Ms. Harris. He performed Eminem’s “Lose Yourself” after the rap star introduced the former president.

An audience member shouted, “I miss you,” and Mr. Obama launched into a defense of the Biden administration’s unpopular track record and why it should not persuade voters to support Mr. Trump.

“I get why people are looking to shake things up. I understand that, but what I cannot understand is why anybody would think that Donald Trump will shake things up in a way that is good for you because there is absolutely no evidence that this man thinks about anybody but himself,” he said.

While ringing up customers at a Macon CVS, Mr. Prescott shrugged off Mr. Obama’s criticisms. He said some Black Americans once considered Mr. Obama the most important figure of their generation, but, unlike Mr. Trump, his time in office produced little for the Black community.

 “As you got older, it was like, what did Barack do?” Mr. Prescott said. “And it’s a hard pill to swallow.”