Republican Matt Van Epps is a military veteran who served nine tours of duty in Iraq and Afghanistan. Photo: Getty Images

With almost all the votes counted, Republican Matt Van Epps was on course to beat Democrat Aftyn Behn by around nine percentage points.

The victory helps Republicans to retain their narrow majority in the House of Representatives, but Van Epps's winning margin looks set to be less than half of what Trump won the district by in the 2024 presidential election.

The vote in the state's 7th Congressional District received national attention as the US looks ahead to midterm elections next year.

The special election was framed by some as a referendum on Trump's performance during his second term so far, and as a bellwether for the 2026 congressional elections, in which the Democrats will attempt to take control in Congress.

Failure to hold the seat would have been seen as an enormous blow for Republicans and an indication that Trump's electoral appeal could be waning.

In the end, the party retained the seat, but with a margin well below the decisive victory Trump achieved there last year.

The congressional seat that was up for grabs stretches from the border of Alabama to Kentucky, and encompasses parts of the city of Nashville. No Democrat has been elected there in over 40 years.

The seat was vacated after Republican Congressman Mark Green resigned in July to work in the private sector.

Both parties spent millions of dollars in an effort to boost their candidate.

Top party officials also visited the state to hold rallies, including former Democrat Vice-Presidents Kamala Harris and Al Gore, and Republican Speaker of the House Mike Johnson.

Van Epps had aligned himself closely with Trump, who held a virtual rally to support his campaign.

Following his victory, Van Epps said the result "showed running from Trump is how you lose, running with Trump is how you win."

"Politicians who run from the president or abandon the common-sense policies that the American people gave us a resounding mandate on do so at their own peril," he added.

Trump congratulated Van Epps on social media on Tuesday night, writing that "the Radical Left Democrats threw everything at him, including Millions of Dollars".

Behn lost in every county except for Davidson County, which contains the city of Nashville.

But at a campaign event on Tuesday night, Behn said that despite her loss, she believed the result was "the beginning of something powerful", adding that "nobody in Washington believed we could get even this close".

Ian Russell, a Democratic operative who consulted for the Behn campaign, told the BBC that Trump "had to spend millions of dollars to hold this seat".

"Republicans went all out to keep this seat. This is a very, very bad sign for them heading into the midterms," he said.

Tennessee is still decidedly Trump terrain. He won the state with 64% of the vote last year and topped 60% the previous two presidential elections.

Van Epps is a military veteran who served nine tours of duty in Iraq and Afghanistan. He ran in a crowded primary where loyalty to Trump was a litmus test – and a last-minute endorsement by the president put him over the top.

Behn, meanwhile, focused her campaign almost exclusively on affordability and local quality of life issues.