Trump declined on Wednesday to embrace a peaceful transfer in response to a reporter's question and said he expected his election battle with Democrat Joe Biden to be settled by the Supreme Court.

The Republican president's exchange with reporters set off a fury that prompted several Republicans in Congress to distance themselves from the president.

Despite nearly four years of incendiary statements by Trump, members of his own party have regularly been loath to criticise him, as many feared political retribution.

"The winner of the November 3rd election will be inaugurated on January 20th. There will be an orderly transition just as there has been every four years since 1792," McConnell wrote in a morning tweet.

Like other Republicans, McConnell did not directly criticise Trump.

By midday, with no sign of the controversy abating, White House Press Secretary Kayleigh McEnany told a news briefing: "The president will accept the results of a free and fair election."

But for months, Trump has cast the November election as being rigged and repeatedly attacked Democrats for promoting the widespread use of mail-in ballots for voters who do not want to risk contracting the deadly COVID-19 virus by casting their ballots at potentially crowded polling centres.

Democrats accused Trump of threatening American democracy and further politicising his upcoming choice to replace the late Supreme Court Justice Ruth Bader Ginsburg by suggesting the yet-to-be named nominee would intervene in the election's outcome.

Some of McConnell's fellow Republicans joined the effort to quell election fears, including Senators Marco Rubio and Mitt Romney and House Republican leader Kevin McCarthy, who told reporters, "It will be a smooth transition regardless of the outcome".

Trump, who trails Biden in national opinion polls, has long sought to cast doubt on the legitimacy of the election, asserting without evidence that mail-in voting would be rife with fraud.

"President Trump, you are not a dictator and America will not permit you to be one," said Senate Democratic leader Chuck Schumer, who took to the Senate floor to call the president "the gravest threat" to US democracy.

Senator Bernie Sanders, an independent who aligns with Democrats and who lost to Biden in the party's presidential nominating race, called for an independent commission to oversee the upcoming election.

Democratic House of Representative Speaker Nancy Pelosi cautioned against panicking over the remarks of a president who she said admires autocratic leaders.

At a news conference, she urged Americans to cast their ballots and admonished Trump: "You are not in North Korea, you are not in Turkey, you are not in Russia."

If November's election is close, Trump could contest the results in federal courts in hopes of being awarded enough Electoral College votes to retain the White House, according to political analysts.

Only one US presidential election, the 2000 contest between Republican George W Bush and Democrat Al Gore, has had its outcome determined by the Supreme Court.

Australian Associated Press