If most Republicans vote in person and most Democrats vote by mail, Hasen said, that could create a scenario well suited to Trump’s tendency to make unfounded accusations of wrongdoing.

“As Trump drives more and more of his supporters to vote in person and away from vote-by-mail, it’s quite likely that we’ll see Trump getting many more votes on election night, the votes that are counted on Election Day,” Hasen said in an interview on “The Long Game,” a Yahoo News podcast.

“Then, four or five days later, [if] Biden becomes the winner as the absentee ballots are counted in Philadelphia or Detroit, that’s a recipe, if it’s close, for a really ugly election scenario,” he said.

Hasen pinpointed Philadelphia and Detroit in particular because they are both big cities in key swing states that decided the 2016 election, and both cities have a track record of what Hasen calls “electoral incompetence” in his book.