NEW YORK — Alarmed by the tight race for a congressional seat in Ohio, Republicans are steeling for a 90-day campaign of trench warfare as they fight to keep control of the House, pinning their hopes on well-funded outside groups and a slashing negative message about Democrats.

Voting across the Midwest and West laid bare the party’s precarious situation on Wednesday: Ohio’s special election exposed deep vulnerabilities in the historically conservative suburbs of Columbus, and the Republican candidate there held a slim lead over his Democratic challenger.

In Kansas, a nomination fight for governor also remained too close to call the day after the primary, with a hard-right candidate threatening to topple the state’s Republican incumbent and splinter the party down ballot.


And in primaries from suburban Detroit to Seattle, Democrats selected hard-charging candidates in districts long held by the Republican Party.

Republicans believe they can maintain a thin grip on the House by propping up incumbent lawmakers in red-tinged districts and branding the Democrats as wildly left-wing. But senior party strategists have concluded that more than a dozen districts held by Republicans may already be unwinnable, most of them in metropolitan areas where President Trump has alienated moderates and stirred volcanic resistance on the left.

The Republicans can afford to lose only 22 seats to maintain even a one-seat majority. That leaves them with little room for error. Veteran party lawmakers have an increasingly bleak view of their prospects in the House, and some fear that Democrats could seize the chamber by a convincing margin.

“There’s a real likelihood that they not only win the House, but they win it by 10 or 12 more seats than they need,” said Senator Lindsey Graham of South Carolina, voicing what many GOP officials have begun to acknowledge privately.

Graham said a Democratic takeover was no sure thing, noting that “in the era of Trump, things can change in 24 hours, for good or bad.” But he said any Republican in a remotely competitive district could face a difficult general election.


“We’re bleeding among women and the enthusiasm factor for Democrats is worth 7 or 8 points, and sometimes more,” Graham said, using political jargon to describe just how deep into Republican territory the battlefield might stretch: “If I was a House guy in an R+10 or less seat I’d be getting on the phone and raising money and putting a sign on my dog.”

In Kansas, Republicans faced uncertainty Wednesday not only about their candidate for governor this fall, but also whether they were creating an opportunity for Democrats to win the office in November. Should the party ultimately nominate Kris W. Kobach, its hard-right candidate for governor, it could also undermine Republicans in congressional races.

With all Kansas precincts reporting Wednesday morning, Kobach, the secretary of state, was ahead of Governor Jeff Colyer by just 191 votes out of more than 311,000 Republican ballots cast. The results were likely to remain in flux for at least several days.

And in another race where Republicans could be vulnerable, Sharice Davids, a lawyer who is Native American, won the Democratic congressional primary Wednesday in a swing district that surrounds Kansas City. She will face Representative Kevin Yoder in the general election. It is one of two Republican-held districts in the state, along with a more rural open seat next door, where Democrats are threatening to shave down the House majority.


In Ohio, the Republican candidate for Congress, Troy Balderson, was ahead by 1,754 votes out of more than 202,000 cast — a lead of nearly 1 percentage point. But 3,435 provisional ballots had yet to be counted. Ohio law provides for an automatic recount if the two candidates are ultimately separated by less than half a percentage point.

The Democratic candidate in Ohio, Danny O’Connor, had not conceded the race and is set to face Balderson again in the November general election.

Illustrating the aggressive approach the Republican Party is taking to reinforcing its candidates in conservative-leaning districts, the Congressional Leadership Fund, the principal super PAC dedicated to House Republicans, has begun airing attack ads against Democratic challengers in three traditionally red seats in Kansas, Kentucky, and upstate New York. Trump carried all three districts in 2016 but Democrats are pursuing all of them ferociously.

Corry Bliss, the group’s chief strategist, said Republicans needed to wage a national campaign to disqualify Democrats as a political alternative in the eyes of voters.

“This is a tough environment and we have to give voters a choice in November,” Bliss said. “One party has cut your taxes and helped create the best economy in decades. The other party says: ‘We will raise taxes, we will abolish ICE, and we will put Nancy Pelosi in charge of it all.’ ”

But Bliss also sent a stern message to lawmakers in his own party who may not be bracing adequately for a fall onslaught by Democrats: “We have to have members who raise money, run good campaigns and provide a good contrast for November,” he warned.


What alarms congressional Republicans, though, is what is out of their hands — not just Trump’s conduct but also some of the controversial candidates leading their tickets. In addition to Kansas, should Kobach prevail, House Republicans are burdened with unpopular standard-bearers in Illinois (Governor Bruce Rauner) and Virginia (a Senate candidate, Corey Stewart) who together could drag down at least a half-dozen lawmakers.

In the Ohio race, some former Republican loyalists defected to O’Connor while other right-of-center voters may simply have stayed home, producing a close outcome in a lopsidedly Republican area. Balderson may have prevailed because just enough conservative voters remain satisfied enough with Trump.