US Republicans narrowly avoided an embarrassing scare on Tuesday, holding a district in deeply conservative Tennessee with a sharply reduced majority that underscored voter unease in one of Donald Trump's safest bastions.

Retired special-operations pilot Matt Van Epps defeated Democrat Aftyn Behn by an eight-point margin, according to projections from The New York Times and CNN -- a steep drop from Trump's 22-point romp in 2024 -- in a race that had unexpectedly tightened into a referendum on the president's standing.

The result in the race for Tennessee's 7th District House seat spared Republicans a political shockwave, but the trimmed margin set off alarms in a party already fretting over its threadbare House majority and the risk of further erosion in 2026.

The Republican winning margin has been between 22 and 47 points in the last seven elections for that seat.

Trump was quick to celebrate Van Epps's victory in multiple posts to his Truth Social platform.

"Congratulations to Matt Van Epps on his BIG Congressional WIN in the Great State of Tennessee. The Radical Left Democrats threw everything at him, including Millions of Dollars," Trump wrote.

The Republican win comes amid a run of Democratic momentum. Just weeks ago, Democrats swept major races in Virginia and New Jersey and won the New York mayoralty, a string of victories widely interpreted as a rebuke to Trump's return to power. (AFP)