WASHINGTON — US President Donald Trump’s Republican Party was on course Wednesday for a stunning defeat in a key special congressional election in Pennsylvania, adding to the turmoil engulfing his administration after the sacking of Secretary of State Rex Tillerson.

Democrats exulted in the stunning performance by one of their own in a race that has taken on national implications, insisting that their unexpectedly strong showing in Trump country -- unthinkable a year ago -- bodes well for them ahead of November’s midterm elections.

With all precincts reporting, and more than 240,000 ballots cast Tuesday, Democratic candidate Conor Lamb was leading Republican Rick Saccone by 579 votes, or 49.8 per cent to 49.6 per cent.

As county officials counted provisional and absentee ballots that willlikely determine the outcome, Lamb declared victory in the wee hours of Wednesday, in a district Trump won by nearly 20 points in the 2016 presidential contest.

The New York Times later called the race for Lamb, saying his lead "appeared insurmountable."

And Lamb’s party swiftly proclaimed that Trump and his Republicans could face a political reckoning this year -- with control of Congress up for grabs.

"As we head into the 2018 midterms, the momentum is undeniable for Democratic candidates running up and down the ballot," Democratic National Committee head Tom Perez said. — AFP