Of all 249 Republicans in the US House and Senate, only 25 told the Washington Post they believed the Democrat won against the US president last month.
Ninety per cent, or 222 other congressional Republicans, refused to answer the Post when it asked them “who won the election?” on Wednesday.
Mr Trump, on the same day, uploaded a widely derided speech to Facebook and Twitter, in which he again alleged that the election had been “rigged” against him, among other conspiracy theories, without basis.
Even as William Barr, the attorney general, had said the US justice department found no widespread election fraud, some 24 hours before Mr Trump’s address was shared online.
And while the president’s own cybersecurity agency at the Department of Homeland Security had determined days after the election that it was more secure than any other in American history.
Still, as little as 9 Republican lawmakers told the Post they supported “Donald Trump’s continuing efforts to claim victory”, while 8 said they opposed the president’s stance, and 232 refused to provide an answer.
Asked whether they would acknowledge Mr Biden as “the legitimately elected president” when the Electoral College votes for Mr Biden, only 30 responded “yes” and two said they would not.
217 congressional Republicans did not respond to the third question in the survey, which was conducted by 25 reporters.
It follows weeks of false allegations by Mr Trump and his allies about the election, which he still has not officially conceded, while Republicans in Congress have stayed largely silent about his claims, despite evidence.