Sean Wilentz, a professor of history at Princeton, was outspoken:

It would be not simply a major departure but a deeply dangerous one were Trump to deny the legitimacy of Biden’s election. It would be a brutal renunciation of American democracy. It would create not simply a fissure but a chasm in the nation’s politics and government, telling his tens of millions of supporters as well as his congressional backers to reject Biden’s presidency. It would be an act of disloyalty unsurpassed in American history except by the southern secession in 1860-61, the ultimate example of Americans refusing to respect the outcome of a presidential election.