Vice President Kamala Harris and former President Donald J. Trump are in an even tighter race in the battlegrounds of Michigan and Wisconsin than just seven weeks ago, according to new polling from The New York Times and Siena College.

Ms. Harris’s advantage from early August has been chiseled away slightly by Mr. Trump’s enduring strength on economic issues, the polls found, a potentially troubling development for the vice president given that the economy remains the most important issue driving voters.

With less than 40 days until Election Day, the race is essentially tied in Michigan, with Ms. Harris receiving 48 percent support among likely voters and Mr. Trump garnering 47 percent — well within the poll’s margin of error. In Wisconsin, a state where polls have a history of overstating support for Democrats, Ms. Harris holds 49 percent to Mr. Trump’s 47 percent.

The polls also found that Ms. Harris had a lead of nine percentage points over Mr. Trump in Nebraska’s Second Congressional District, whose lone electoral vote could be decisive in the Electoral College. In one possible scenario, the district could give Ms. Harris exactly the 270 electoral votes she would need to win the election if she carried Michigan, Wisconsin and Pennsylvania and Mr. Trump captured the Sun Belt battlegrounds, where Times/Siena polls show he is ahead.

[We’ve had a lot of close elections in recent memory, but in none of them were the polls so close, Nate Cohn writes.]

The Times and Siena College also tested the presidential race in Ohio, which is not considered a battleground for the White House but has one of the country’s most competitive Senate races. Mr. Trump leads by six points in Ohio, while Senator Sherrod Brown, a Democrat, is ahead of his Republican opponent, Bernie Moreno, by four points.

Wisconsin, which has for months appeared to be a bright spot for Democrats on the presidential battleground map, has been decided by less than a point in four of the last six campaigns, including 2020. Mr. Biden won Michigan by three points that year after Mr. Trump carried it by three-tenths of a point in 2016.

Mr. Trump remains broadly disliked, but interviews with those polled show that Ms. Harris faces a challenge in winning over voters who cannot bring themselves to support the former president.

“I’m not a happy camper,” said Matt Henderson, 65, a maintenance man for the local electric company in Westland, Mich. He said he was likely to vote for Ms. Harris not because he was politically drawn to her but to prevent Mr. Trump from returning to power.

“Jan. 6, 2021, proved he is a traitor,” Mr. Henderson said. “He doesn’t care about anything but himself. He tried to steal an election.”

The polls found that 80 percent of Black voters across Michigan, Wisconsin and Ohio were planning to vote for Ms. Harris, and 13 percent for Mr. Trump. An additional 7 percent of Black voters said they did not know how they would vote. While Ms. Harris has a huge edge among Black voters, the 80 percent figure is less than Mr. Biden won nationally four years ago.

Antonio Dawkins, 40, a regional sales manager from Waukesha, Wis., a suburb of Milwaukee, said he planned to vote but would leave the presidential line blank. He dislikes Mr. Trump but is also dissatisfied with Ms. Harris.

“She’s kind of taking the car salesman pitch and trying to sell everybody that she’s not Trump, and that’s not enough,” said Mr. Dawkins, who is Black. “She says a lot of things that sound good with no details. So I guess they call that — there’s no meat and potatoes.”

The polling results fit a recurring theme with voters in battleground states: Many tend to believe that Mr. Trump’s time in office helped people like them, and they worry that Ms. Harris’s policies would hurt people like them.

In Michigan and Wisconsin, voters were about equally likely to say Ms. Harris’s policies would help as they are to say her policies would hurt: 41 percent versus 40 percent. But 46 percent of voters in the two states said Mr. Trump’s policies would help people like them.

Yet when voters in Michigan and Wisconsin were presented with a direct head-to-head question about which candidate they trusted more to “help people like you,” Ms. Harris had a slight edge, suggesting that voters drew a subtle distinction between the candidates and their policies.

Voters in the states were also tied on which candidate they trust more to help the working class.

After the economy, abortion was the second most important issue to voters in Michigan and Wisconsin, with 18 percent saying it was central to their choice. That is an increase from May, when 13 percent of voters in the two states said abortion was their top issue.

On abortion, voters in Michigan preferred Ms. Harris to Mr. Trump by 20 points and in Wisconsin by 13 points. In Wisconsin, though, that is down from a 22-point advantage in August. In Michigan, Ms. Harris’s numbers on abortion are largely unchanged.

Mr. Trump’s biggest vulnerabilities relate to his comportment. In Wisconsin, 55 percent of undecided and persuadable voters cited his behavior, his honesty and his ability to serve as president as among their chief concerns. In Michigan, the number was lower, at 47 percent.

“He’s divisive, he’s violent, he’s vile,” said Lesley McKenzie, 64, an executive assistant from Southfield, Mich. “He’s unbecoming to even sit or even to pass by the White House. I mean, it’s totally crazy.” She added: “He is like rolling in a pigsty. Every day he comes up with crazy things. I don’t think he’s all there. And if he is, oh my God.”

The crucial group of voters who could decide the election — undecided and persuadable Americans — has shrunk slightly since August as they begin to solidify their decisions.

In Michigan and Wisconsin, these voters leaned slightly toward Ms. Harris, though they have reservations about both candidates. Roughly a third said their primary concern about Mr. Trump is his personality, while 12 percent worried about whether he could actually do the job and 8 percent were apprehensive about his honesty and truthfulness.

Nathan Booth, 27, a surgical resident from the Detroit suburbs, called Mr. Trump’s debate performance this month “embarrassing.” Dr. Booth said he voted for Mr. Trump in 2016 and then for Mr. Biden in 2020 because of the Republican president’s behavior.

Despite those feelings, Dr. Booth said he was inclined to vote for Mr. Trump again this year because of his dissatisfaction with Mr. Biden’s handling of the economy.

“In the last three years, my purchasing power has gone down,” he said. “I have less money than I did before, and I imagine that the majority of the country making under $100,000 is feeling the same way.”

Fewer undecided and persuadable voters had concerns about Ms. Harris’s personality and temperament. Just 10 percent in Michigan and Wisconsin said her personality or judgment were their main concern, while 19 percent worried about her honesty and truthfulness.

The polls also offer a window into how the vice-presidential candidates are viewed in the Midwest, particularly in Ohio, the home state of Mr. Trump’s running mate: Senator JD Vance.

In the three states polled, 49 percent of voters viewed Ms. Harris’s running mate, Gov. Tim Walz of Minnesota, as honest and trustworthy, compared with 45 percent for Mr. Vance. Even in Ohio, Mr. Walz was viewed as more honest and trustworthy.

Across the Midwest, Mr. Walz was seen as more caring, but in Ohio, slightly more voters saw Mr. Vance as someone who “cares about people like me.”

The polls showed that concern about immigration is more prevalent in Ohio, where Mr. Vance and Mr. Trump have drawn attention for amplifying false claims that Haitian immigrants in the city of Springfield were killing and eating pets.

Ohio voters were less likely than their neighbors in Michigan and Wisconsin to say that America’s openness to people from around the world is essential to who we are as a nation, though a majority of the state’s voters still said this.

Here are the key things to know about these polls

• Interviewers spoke with 688 likely voters in Michigan, 687 likely voters in Ohio, 680 likely voters in Wisconsin and 680 likely voters in Nebraska’s Second Congressional District from Sept. 21 to 26, 2024.

• Times/Siena polls are conducted by telephone, using live interviewers, in both English and Spanish. Overall, about 97 percent of respondents were contacted on a cellphone for these polls. You can see the exact questions that were asked and the order in which they were asked here.

• Voters are selected for the survey from a list of registered voters. The list contains information on the demographic characteristics of every registered voter, allowing us to make sure we reach the right number of voters of each party, race and region. For these polls, interviewers placed nearly 260,000 calls to just over 140,000 voters.

• To further ensure that the results reflect the entire voting population, not just those willing to take a poll, we give more weight to respondents from demographic groups that are underrepresented among survey respondents, like people without a college degree. You can see more information about the characteristics of respondents and the weighted sample at the bottom of the results and methodology page, under “Composition of the Sample.”

• The margin of sampling error among likely voters is about plus or minus four percentage points for each poll, and about plus or minus 2.5 percentage points when the three state polls are joined together. In theory, this means that the results should reflect the views of the overall population most of the time, though many other challenges create additional sources of error. When the difference between two values is computed — such as a candidate’s lead in a race — the margin of error is twice as large.