Peltola leads by just 637 votes in Alaska, as the Democratic Senate majority could stretch to 56

Energised by sweeping midterm victories, Democrats were on Thursday eyeing the possibility of adding still more seats to their congressional majorities, particularly in Alaska and Mississippi, where they hope to flip Republican-held Senate seats.

In Alaska, former Representative Mary Peltola, a Democrat, was leading her Republican opponent, Senator Dan Sullivan, by 637 votes with 78 percent of the vote tallied. The bulk of the remaining ballots were expected to be mail-in votes, which tend to favour Democrats, but the race will proceed to a ranked-choice tabulation on Nov. 18 if no candidate reaches 50 percent of the vote.

In Mississippi, Scott Colom, a Democratic prosecutor, was leading Senator Cindy Hyde-Smith by roughly 1,130 votes. But Mississippi's secretary of state said about 3,600 absentee-by-mail ballots were still to be received in the coming days, plus an 'unknown number of affidavit ballots'.

The Democratic majority in the Senate could stretch to 56 seats if their candidates win both races, though such results are far from assured, the report said. Neither contest has been called, and it could be days or weeks until either is decided.

In the House, Democrats are on track to secure at least a 50-seat majority, and the party maintained hope of adding to that number as more ballots were tabulated in close races.

Two days after a lopsided election, Democrats were preparing to serve as a check on President Trump during his final two years in office, begin investigations into the administration's efforts to curb renewable energy development and scrutinise the president's enrichment of himself and his family.

Representative Robert Garcia, the California Democrat who is set to lead the House Oversight Committee, warned after the Democratic landslide became clear: 'Lawyer up.'

Republicans, meanwhile, were grappling with sweeping defeats. Speaker Mike Johnson told Republican aides on Wednesday that he would not seek to lead the Republican conference in the House when the party entered Congress next year in the minority, setting up a leadership battle between Representatives Steve Scalise of Louisiana and Jim Jordan of Ohio, both of whom quickly said they would run for minority leader.

Party leaders were also assigning blame for their dismal results. Vice President JD Vance said the conflict in Iran, which has caused a surge in gas prices, was at fault: 'The reason we lost is the war,' he wrote on social media. Mr Trump said Mr Vance's assessment was 'largely true', but insisted: 'If I had to do it again, I'd have to do it again.'

Senator Susan Collins, a Republican whose three-decade career came to an end when Democrats flipped her seat in Maine, said she got 'caught up in the Trump tsunami' as voters who would otherwise have backed her sought to send a message to the president.