US Republican leaders say there will be an “orderly” transfer of power should Donald Trump lose November’s election.
President Trump cast doubt on the transition on Wednesday, questioning the probity of the vote with so many ballots likely to be cast by mail.
But Republican Senate leader Mitch McConnell said there would be a peaceful handover in January as there had been every four years since 1792.
Democratic senators label Mr Trump a grave threat to American democracy.
The president currently trails his challenger, Democrat Joe Biden, in national opinion polls with 40 days to go until the election.
Many more Americans than usual will be casting their votes by post this year, due to the pandemic, and Mr Trump has been questioning the security of this mail-in ballot system.
If Mr Trump were to refuse to accept the result of the election, it would take the country into uncharted territory.
Mr Biden has suggested that should this happen, the military could remove Mr Trump from the White House.
However, Mr Trump’s spokeswoman said the president would abide by the results of a free and fair election.