A group of prominent American historians added their voice on Monday to the debate about President Trump’s effort to overturn the election, decrying what they called an undemocratic bid to unravel a free and fair vote that has no historical precedent in the long annals of the United States.

“Never before in our history has a president who lost re-election tried to stay in office by subverting the democratic process set down by the Constitution,” the historians said in a statement. “That is what President Trump has been doing since November 3, when a strong electoral majority of Americans chose Joseph R. Biden to be the 46th president of the United States.”

The historians’ statement pointed out that the 2020 election was not even particularly close in historical terms. Mr. Biden won as many or more Electoral College votes as the winning candidates in five elections since 1960 and larger popular majorities than in more than half of the presidential elections held in the last six decades.

“Yet in none of these elections did any losing candidate attempt to claim victory by brazenly sabotaging the electoral process as Donald Trump has done and continues to do,” said the letter, organized by Douglas Brinkley of Rice University and Sean Wilentz of Princeton University.