DERRY, N.H. — With Republican control of the U.S. Senate hanging in the balance, incumbent Republican Sen. Kelly Ayotte had a slim lead over Democratic New Hampshire Gov. Maggie Hassan late Tuesday night.

Ayotte was leading Hassan by about 12,000 votes, with 65 percent of the precincts reported, according to CNN.

“We’re doing very well in the great state of New Hampshire tonight,” said Jennifer Horn, chairwoman of the New Hampshire Republican Party, to a crowd of several hundred supporters at the Grappone Hall in Concord, N.H. “How many people want to send Kelly Ayotte back to Washington?”

Recent polls had shown Hassan and Ayotte deadlocked in the final months of the election.

The race was among a handful across the country expected to determine whether Republicans could hold onto power in the Senate. Republicans had a 54 to 46 seat advantage before the election; Democrats needed to pick up five Republican seats to get a majority.

Throughout the New Hampshire campaign, Hassan blasted Ayotte as a Washington insider and Donald Trump supporter who repeatedly voted to end Medicaid expansion under the Affordable Care Act, which covers substance abuse and mental health treatment.

She cited Ayotte’s votes to “shut down the federal government” and defund Planned Parenthood over abortion funding.

Ayotte, meanwhile, called Hassan a “hypocrite” for initially vetoing the state budget, saying the action delayed funding aimed at addressing the state’s heroin crisis and helping those struggling with mental illness.

Jill Domosh, of Derry, said she voted for Ayotte because she’s concerned about rising healthcare costs.

Domosh, 62, runs a commercial floor installation business with her husband and said her health insurance costs have gone from $400 to $1,500 a month, putting a squeeze on her family’s business. She wants Congress to repeal the federal Affordable Care Act.

“Obamacare has killed us,” she said after casting a ballot at the Gilbert H. Hood Middle School in Derry, where a steady stream of voters converged on the polls Tuesday. “It was the dumbest thing this country has done, ever. We need to get rid of it.”

For Hassan supporter Leonard Whitney, his ballot was less a vote for the governor than it was a vote against Ayotte.

“Anyone who looks at Donald Trump as a role model is problematic for me,” the Derry man said. “She’s part of what is the worst Congress in history. I’d like to see the Democrats take control of the Senate, which I think would ease some of the gridlock.”

Ayotte’s reluctance to support federal gun control legislation was another big turn-off.

“There’s a lot of people in New Hampshire who want sensible gun control, and she doesn’t seem interested in hearing that,” he said.

In the final days of the race, Hassan’s campaign enlisted dozens of Democratic surrogates from Massachusetts — including Sen. Elizabeth Warren and Rep. Seth Moulton — who spent much of the past weekend campaigning in New Hampshire.

President Barack Obama held a rally in Durham on Monday, tethering Hassan’s Senate bid to Hillary Clinton’s White House campaign.

“Maggie Hassan will make sure we’ve got a Democratic majority to work for the things you care about,” Obama told the crowd. “If you care about creating jobs, if you care about childcare they can afford, if you care about equal pay for women and a higher wages for workers, then you’ve got to vote for Democrats up and down the ticket.”

Ayotte’s reelection bid was dogged by criticism over her support — and non-support — for the Republican presidential nominee.

Earlier this year, Ayotte and fellow Republican House Speaker Paul Ryan of Wisconsin and Sen. John McCain of Arizona criticized Trump, who refused to support them for re-election. Facing pressure, Trump relented several months later and endorsed all three.

During a debate in October, Ayotte told a moderator that Trump would be a role model for her children but walked back her comments hours later. Then she told reporters that she would write in Republican Vice President candidate Mike Pence’s name on the ballot.

Hassan’s campaign seized on Ayotte’s comments, putting out last-minute campaign ads criticizing her support for Trump.

The race was noted for one of the highest shares of out-of-state spending of all Senate contests in the country, with 95 percent of the $81 million spent so far coming from outside New Hampshire, according to a report by the nonprofit U.S. Public Interest Research Group.

Hassan’s and Ayotte’s campaigns spent another $34 million on the race combined, according to campaign finance reports.

The record-setting spending paid for a relentless blitz of negative TV ads in the final weeks of the election.

On Tuesday, Hassan and Ayotte supporters said they were equally dismayed by the negative tone of the race.

“Hated it, absolutely hated it,” said Yvonne Macgilvery, an independent from Derry, who voted for Hassan. “I’m so glad it’s over.”

Christian Wade covers the Massachusetts Statehouse for CNHI’s newspapers and websites. Reach him at cwade@cnhi.com