The Vermont Republican Party has dismantled Democrats’ supermajority in the Vermont Senate, unseating four incumbents and dominating races for open seats.

Republicans toppled Democratic incumbents in the Addison, Orange, Chittenden-North and Grand Isle districts, according to unofficial results provided by the Secretary of State’s Office, and they picked up another two open seats that are being vacated by long-serving Democrats in Orleans and Caledonia counties.

In total, the GOP has nearly doubled its representation in the upper chamber, from seven seats last session to 13. That means Democrats and Progressives, who held 23 seats, will now control 17 — and will no longer have the two-thirds majority needed to override gubernatorial vetoes. (A similar dynamic played out in the Vermont House, where Democrats also lost their supermajority.)

The Addison result proved the chamber’s biggest upset of the evening, with Sen. Chris Bray, chair of the Senate Committee on Natural Resources and Energy, losing to relative political newcomer Steven Heffernan in a district thought to be solidly Democratic.

Preliminary results from the Secretary of State’s Office for that district showed Sen. Ruth Hardy, D-Addison, with 23.47%, closely followed by Heffernan with 23.34% and Bray with 22.04%.

In the Orange County race, Republican Larry Hart, a building supply store salesman, definitively took down Sen. Mark MacDonald, a Democrat who has served in the Legislature for a combined total of more than 30 years. Hart won 54% of the vote to MacDonald’s 42%, according to the preliminary results Tuesday night.

From Gov. Phil Scott’s election night party, Vermont Republican Party Chair Paul Dame said of the GOP’s down-ballot success, “I don’t think we’ve had a night this good in 10 years.”

“During the last two years, we kind of had this stalemate, with the governor saying, ‘I’ve got a mandate with 70% of the vote,’ and (House Speaker Jill) Krowinski and (Senate President Pro Tempore Phil) Baruth saying, ‘We’ve got a mandate with a supermajority.’ And there’s sort of been this impasse,” Dame said. “Tonight, voters have weighed in on how to solve that stalemate. They said, ‘You should have been listening to the governor in (the) last two years.’“

Meanwhile, as results began to come in at the Vermont Democratic Party’s election night gathering in South Burlington, Baruth told the crowd there, “I’m not going to lie to you — this is a tough night.”

The party’s executive director, Jim Dandeneau, was similarly downtrodden. “We are not seeing the results locally that we had hoped for,” he said shortly after 10 p.m. In an interview an hour later, he said that the state GOP’s — and particularly Gov. Scott’s — messaging over property taxes proved to be more effective than what he called Democrats’ “herculean work” knocking on doors and engaging with voters on the ground.

“He was blanketing the airwaves with his messaging about cutting taxes. That ended up being not great for us.”

By around 9 p.m., the GOP had flipped its first seat, with Rep. Patrick Brennan, R-Colchester, ousting recently appointed Democratic Sen. Andy Julow in the Grand Isle district.

Brennan, a longtime member of the Vermont House, carried the seat with 51% of the vote to Julow’s 45.6%, according to preliminary results from the Secretary of State’s Office.

Julow, of North Hero, was appointed to fill the late Sen. Dick Mazza’s seat in the single-member district in May. Mazza, a moderate Democrat, held the seat for decades before his death this year. Both candidates modeled themselves after the late dean of the Senate.

By 9:30 p.m., Republicans had picked up another seat, this time when Rep. Chris Mattos, R-Milton, won the Chittenden North district.

Sen. Irene Wrenner, D-Chittenden North, sought to defend her seat after winning the newly created battleground district two years ago.

Driven by a dominant showing in Milton and Fairfax, Mattos garnered 54% of the vote to Wrenner’s 42%, according to preliminary results from the Secretary of State’s Office.

The race marked the Vermont Republican Party’s second go at Chittenden County’s northernmost Senate district, which has been a target for the party since reapportionment in 2022 broke up the former six-member Chittenden County district into three parts.

Republican candidates also clinched seats in two Northeast Kingdom counties Tuesday night. In Caledonia County, Republican Rep. Scott Beck will replace outgoing Democratic Sen. Jane Kitchel, who has long chaired the powerful Senate Appropriations Committee.

Beck collected 56% of the vote to Democrat Amanda Cochrane’s 40%, according to preliminary results from the Secretary of State’s Office.

“Vermonters have clearly spoken and said that this state is becoming unaffordable for far too many,” Beck said in an interview at Gov. Scott’s election party in Montpelier. “They’re telling us that they don’t want the far extreme agendas. They want the middle to be represented again.”

In neighboring Orleans County, Republican Sam Douglass, a local GOP leader from North Troy, similarly declared victory over Rep. Katherine Sims, D-Craftsbury. He will fill outgoing Democratic Sen. Bobby Starr’s seat.

“Up in the Northeast Kingdom, we’re a very tight knit bunch, and we know when you’re not authentic,” Douglass said in an interview Tuesday night. “This might be a little radical to say, but I don’t think it was Republicans that won. I think it was common sense that won.”

Douglass secured 56% of the vote to Sims’ 38%, according to the Secretary of State’s Office’s preliminary results.

The deaths and departures of six incumbent Democrats this year created an opportunity for Republicans to chip away at the other party’s strength. And in a number of districts, Democratic incumbents faced steep competition.

In April, Mazza stepped down from his Grand Isle seat. And in June, Sen. Dick Sears, a longtime Bennington County Democrat, died. The retirements of Sens. Brian Campion, D-Bennington, Dick McCormack, D-Windsor, Kitchel and Starr presented additional opportunities for newcomers to join the upper chamber.

The open seats, several of which were in purple districts, became a particular focus of the Vermont Republican Party, which sought to end Democrats’ supermajority and allow Republican Gov. Phil Scott to veto bills without being overridden.

What were seen as the five most competitive Senate races, in the Caledonia, Chittenden North, Grand Isle, Orange and Orleans districts, garnered tens of thousands in donations from wealthy Burlington-area families.

Scott campaigned harder than in recent years for fellow party mates, including in the five high-spending races.

Shaun Robinson and Sarah Mearhoff contributed reporting.