CHARLOTTE, N.C. — Voters in a Republican-leaning North Carolina congressional district will choose a new representative on Tuesday in a special election that will test President Trump’s clout ahead of 2020 and Democrats’ ability to make inroads with the sort of suburban voters who propelled them to the House majority last year.
The polls close at 7:30 p.m.
The race pits Dan McCready, a Democrat and Marine veteran whose motto is “country over party,” against Dan Bishop, a Republican state senator who has been endorsed by Mr. Trump and welcomed the president’s characterization of Mr. McCready as an “ultra liberal” who “really admires socialism.”
Putting his political capital on the line, Mr. Trump campaigned with Mr. Bishop on Monday evening in Fayetteville, in the conservative eastern edge of the district, just hours before polls opened. And Vice President Mike Pence also lent a hand on Monday, holding a rally in Wingate, N.C., on Mr. Bishop’s behalf.
The Ninth District covers part of Charlotte and a number of exurban and rural counties to the east. It has not been represented by a Democrat since the early 1960s, and Mr. Trump won it by nearly 12 percentage points in 2016. But in the midterms of 2018, Mr. McCready, surfing the national anti-Trump mood, ran a close race, losing by 905 votes to the Republican candidate at the time, Mark Harris.
Then came one of the more bizarre plot twists in recent American politics: The state elections board threw out the entire election and ordered a new one after evidence surfaced that Mr. Harris’s campaign had funded an illegal vote-harvesting scheme in rural Bladen County.
Mr. McCready, 36, a businessman, decided to keep running, and has now been on the campaign trail for 27 straight months. A centrist, he has been focusing on the issue of health care affordability and criticizing Mr. Bishop for opposing the expansion of Medicaid under the Affordable Care Act.
Mr. Bishop, 55, a Charlotte lawyer, is perhaps best known statewide for sponsoring the controversial so-called bathroom bill that required transgender people to use restrooms that corresponded with the gender on their birth certificate. He boasts of his endorsement from the National Rifle Association, and he has repeatedly attacked Mr. McCready by lumping him with the more left-leaning elements of the Democratic Party.
Mr. Trump has tweeted his endorsement for Mr. Bishop and sent out a fund-raising email on his behalf. In July, Mr. Bishop spoke at Mr. Trump’s rally in Greenville, N.C., in which the crowd responded to the president’s attacks on Representative Ilhan Omar, a Somali-born Democrat, with chants of “send her back!”
The election is effectively the last campaign of the 2018 season, and what alarms national Republicans is how ominously it recalls the midterm elections: As with so many races last year, a centrist Democrat has raised significantly more money than the Republican candidate in a historically conservative district that is now tilting toward the political center because of the suburban drift away from the G.O.P.
And just as in so many of the special elections leading up to Democratic victories, or near-wins, since 2017, local Republicans have beckoned Mr. Trump and Mr. Pence to compensate for the disparity in enthusiasm between the two candidates.
But as officials in both parties recognize, the president is not just a turnout lever for Republicans — he also inspires Democrats and some left-leaning independents.
With Democrats aggressively banking early votes and Mr. McCready enjoying a sizable fund-raising advantage until outside conservative groups rushed in advertising, Republicans had little choice but to call in 11th-hour reinforcements.
A Republican loss after such a presidential intervention would sow doubts about Mr. Trump’s appeal in a state his re-election campaign is depending on. But it could prove even more worrisome to the House G.O.P. A number of incumbent Republicans were already choosing to retire rather than run again in a year when Mr. Trump will be on top of the ticket and their chances of retaking the majority look increasingly poor.
Were Mr. Bishop to lose or even win narrowly, it might trigger a fresh wave of congressional Republican retirements: 15 House Republican lawmakers have already said they will not seek re-election.