President Trump’s unpopularity fuels a clear lead for Democrat Jennifer T. Wexton over Rep. Barbara Comstock (R), putting a prized Northern Virginia district within reach for Democrats for the first time in almost four decades, a new Washington Post-Schar School poll finds.

A month before the midterm election, Wexton, a state senator and former prosecutor, is ahead by 12 points, 55 percent to 43 percent, among likely voters.

In the survey, likely voters say the president is the most important factor influencing their choice for Congress, more so even than the strong economy, which would boost the party in power in a typical election year.

Instead, Trump’s approval rating is weaker in the 10th District, 35 percent, than in a parallel survey of competitive House districts across the nation, which finds 43 percent approve of the president.

In Virginia’s 10th District, 87 percent of voters who disapprove of Trump support Wexton, while 98 percent of those who approve of the president support Comstock.

While Trump’s promise to “drain the swamp” may rally voters elsewhere in the country, it has the opposite effect in the 10th District, where about 3 in 10 likely voters are or live in households with federal government employees or contractors.

Wexton has the edge among these voters, with 61 percent supporting her, while 37 percent support Comstock.

“The data make it clear this election so much is about the president, and that’s a big challenge for Comstock in running for reelection,” said Mark J. Rozell, dean of the Schar School of Policy and Government at George Mason University.

Virginia state Sen. Jennifer Wexton won the Democratic nomination for the state's 10th District on June 12, and attacked her opponent Rep. Barbara Comstock (R). (Jordan Frasier/The Washington Post)

The Post-Schar School poll was conducted by sending mailed invitations to randomly selected registered voters in Virginia’s 10th District identified through official voter records. Respondents had the option of completing the self-administered survey by computer, mobile device or phone. The margin of sampling error among 866 likely voters is plus or minus 4 percentage points.

The poll was conducted from Sept. 19 through Oct. 5, mostly before Comstock’s Republican colleagues credited her last week with pushing their leadership to raise federal wages, in defiance of Trump.

Wexton’s advantage in the Post-Schar School survey is at least slightly larger than in two other surveys conducted in the past month. A Monmouth University poll conducted Sept. 26-30 found Wexton with a six-point advantage, within the margin of error, while the Democrat held a seven-point advantage in a Christopher Newport University survey Sept. 23-Oct. 2.

Comstock, the two-term congresswoman, has at key moments separated herself from the president while focusing on constituent services and issues of local interest.

She has come out strongly against federal government shutdowns and for Metro funding, while talking about the danger posed by the criminal gang ­MS-13, which law enforcement blames for several grisly killings in the capital region. The congresswoman’s ads call her an “independent voice.”

Yet slightly more voters rate her unfavorably than favorably, 47 percent to 40 percent.

Wexton has a better favorable-unfavorable rating, 44 percent positive to 32 percent negative, but a full one-quarter of likely voters haven’t heard of her or have no opinion of her.

The Democrat has touted her work as a state lawmaker to help expand Medicaid and prevent domestic abusers from possessing firearms, among other things.

But her biggest selling point among voters may be the fact that she’s a Democrat.

“You have a very strong anti-Trump environment,” Rozell said, “and so it appears that any credible person with a D next to her or his name is probably going to win the district.”

Wexton maintains a commanding lead in the Post-Schar School poll because of voters like Sonia Heitsch, a 56-year-old retired nurse who moved to Haymarket with her husband a year ago after he retired from the military.

“I am so upset at what is going on in our country with Trump,” she said. “Poor Wexton, it’s not because she’s so outstanding; it’s because she’s a Democrat, if I’m going to be honest.”

Wexton has tried to paint Comstock as a Trump ally who votes with him most of the time. One of her ads calls the congresswoman “Barbara Trumpstock.”

Comstock supporters say the congresswoman overperformed Trump by 16 points on the margin in 2016 and can overcome his drag on the race again this year. The poll shows that her level of support is eight points higher than Trump’s approval mark, yet she still trails Wexton.

The 10th District includes all of Loudoun County and parts of Fairfax and Prince William counties, as well as all of Clarke and Frederick counties and the city of Winchester to the west.

The data shows that self-described independent voters favor Wexton by a 24-point margin, 60 percent to 36 percent, while each candidate receives support from at least 90 percent of likely voters from her own party.

Juan Restrepo, a conservative voter from Trump’s home borough of Queens who now lives in South Ridge near Dulles Airport, said he can’t support Wexton because she wants to roll back corporate tax cuts and supports gun control.

The 44-year-old father of two likes that Comstock introduced a bill to provide paid parental leave for federal workers like himself. He said he will vote for Comstock and stands by his vote for Trump.

“If there’s something true about New Yorkers, we’re a little imprecise with our words,” he said. “We exaggerate a little. I understand that about him. I think his heart is in the right place.”

But Paul Burger, a 44-year-old self-employed industrial hygienist who assesses indoor air quality and lives in Frederick County, has the opposite view. He’s voting for Wexton because he wants to help Democrats take control of the House, in order to — he hopes — start impeachment proceedings and enact gun control.

“I seem to hear a blind approval of everything Trump does from the Republican side, and that just bothers me,” he said. “President Trump is a dangerous president. I think he’s absolutely out of his mind.”

He moved from Buffalo almost a decade ago to escape high taxes and what he called the welfare state, but low unemployment and economic growth do not engender his support for the GOP.

In the Post-Schar School poll, about half of likely voters say health care, immigration, the economy and gun violence are “extremely” important to their vote for Congress, while a larger 64 percent name Trump, and 63 percent say the Supreme Court and other judicial nominations.

A minority of likely voters say special counsel Robert S. Mueller III’s investigation or international trade are extremely important to their vote.

Asked to choose a single issue mentioned in the poll as most important, 35 percent say Trump, 19 percent the economy, 13 percent judicial nominations, 10 percent for both immigration and health care, 6 percent for both gun violence and Mueller, and 1 percent for international trade.

Likely voters in the 10th District are more positive about the nation’s economy, with 84 percent calling it “good” or “excellent,” than in battleground districts generally, where 77 percent say the same. The same holds true of voters asked about their family’s financial situation.

Geoffrey Hoyt, 44, an IT consultant who lives in Frederick County, supports the president because there’s more money in his paycheck, his 401(k) is doing well and foreign trade agreements are being negotiated, although he doesn’t care for Trump’s use of Twitter.

“I like that he doesn’t mince words,” Hoyt said. “I consider myself a pretty smart person and can understand and read between the lines. He takes no BS from anybody. He’s done pretty much everything he’s promised to do.”

Unlike most of the district, Hoyt also opposes restrictions on the Second Amendment. The poll finds 64 percent of likely voters favor stricter gun-control laws, and 29 percent oppose them.

Heitsch, the Wexton voter from Haymarket, tries to persuade her husband to get rid of his guns every time they move, to no avail.

“To me, they represent evil,” she said. “What is a gun made for? It’s to kill things. You can’t sew with them; you can’t cook with them. I’d rather not have them in my house.”

She said she has always voted but kept only an “ear” on political news.

“More and more, my whole body’s in,” she said.

Scott Clement contributed to this report.