WASHINGTON - Republican Dan Bishop won a North Carolina congressional seat Tuesday in a special election that served as a test for President Donald Trump ahead of his bid for a second term in 2020.

With 99 percent of precincts reporting, Bishop won 50.81 percent of the vote against 48.59 for Democrat Dan McCready, a former US Marine who had positioned himself as the moderate in the race, the final election of the 2018 midterm cycle.

The do-over stems from election fraud in 2018.

Trump and Vice President Mike Pence were each in North Carolina's ninth district Monday urging high turnout for Bishop, a state senator who narrowly won a seat that has been safely in Republican hands for half a century.

"Dan Bishop was down 17 points 3 weeks ago," the president tweeted after major US media called Bishop's victory. "He then asked me for help, we changed his strategy together, and he ran a great race. Big Rally last night."

"BIG NIGHT FOR THE REPUBLICAN PARTY. CONGRATULATIONS TO ALL!" Trump wrote, also referring to Republican victories in a separate North Carolina race and a US Senate race in Nebraska.

Republican Mark Harris narrowly led the original November contest against McCready by just 905 votes. But authorities refused to certify the results due to apparent tampering of absentee ballots by operatives tied to Harris.

Ten months later, a McCready victory would have been a historic upset in the district, which voted for Trump by a 12-point margin in 2016.

The district's Charlotte suburbs have shifted increasingly blue during the Trump era, and late Tuesday brought McCready within a hair's breadth of victory, just like in last year's vote.

The president made an 11th-hour appeal before the vote, testing a message he and the party will use in 2020: that extremist Democrats intend to reshape the US economy and society.

"A vote for any Democrat in 2020 and a vote for any Democrat tomorrow in North Carolina is a vote for the rise of radical socialism and the destruction of the American dream," Trump told a crowd Monday in Fayetteville.

The showdown was closely watched by both sides for clues about next year's presidential race and congressional battles. -AFP