Danger signs for Republicans after possible shock loss in election

Conor Lamb's performance in special election in Pennsylvania suggests a Democratic wave in November's midterms

US President Donald Trump's Republican Party is on course 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 remarkable 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.

The race has not yet been officially called - 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.

With county officials counting provisional and absentee ballots that will likely determine the outcome, Mr Lamb declared victory in the wee hours of Wednesday, in a district Mr Trump won by nearly 20 points in the 2016 presidential contest.

And Mr Lamb's party swiftly proclaimed that Mr 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. "Pennsylvania is just the beginning."

The performance by Mr Lamb - a 33-year-old former federal prosecutor and US Marine officer - was an eye-opener on multiple fronts.

Not only did it show Democrats have reconnected with organised labour, it demonstrated that moderates who fought for economic fairness could resonate with older, white, male working-class voters - the very segment of America's electorate that swung to Mr Trump in 2016.

Sombre Republican leaders were forced to acknowledge that, regardless of the eventual outcome, Mr Lamb had dealt a sharp blow to their prospects of maintaining control of the Senate and House of Representatives.

"This should be a wake-up call," House Speaker Paul Ryan told Republican lawmakers in a closed-door conference, according to a person in the room.

Speaking to reporters, however, Mr Ryan sought to downplay the impact, suggesting Mr Lamb was a Democrat unusually well-suited for his district, who ran a pro-life, pro-gun, anti-establishment campaign.

"Both of these candidates ran as conservatives," Mr Ryan said of Mr Lamb and Mr Saccone. "I just don't think you're going to see that across the country" in November.

Democrats exulted over the political ramifications of having potentially ousted a Republican in a conservative, working-class bastion.

"The results in Pennsylvania spell disaster for Republicans in November," said Mr Bradley Beychok, who heads the pro-Democrat political action committee American Bridge.

"If they can't win in a longtime Republican stronghold, no district is safe."

All 435 House seats are up for election every two years. Senate terms are for six years, and 35 of the 100 seats are in play in November.- AFP