From the Guardian:

There is a long-shot legal theory, floated by Republicans before the election, that Republican-friendly legislatures in places such as Michigan, Wisconsin, and Pennsylvania could ignore the popular vote in their states and appoint their own electors. Federal law allows legislatures to do this if states have “failed to make a choice” by the day the electoral college meets. But there is no evidence of systemic fraud of wrongdoing in any state and Biden’s commanding margins in these places make it clear that the states have in fact made a choice.

“If the country continues to follow the rule of law, I see no plausible constitutional path forward for Trump to remain as president barring new evidence of some massive failure of the election system in multiple states,” Richard Hasen, a law professor at the University of California, Irvine, who specializes in elections, wrote in an email. “It would be a naked, antidemocratic power grab to try to use state legislatures to get around the voters’ choice and I don’t expect it to happen.”

For lawmakers in a single state to choose to override the clear will of its voters this way would be extraordinary and probably cause extreme outcry. For Trump to win the electoral college, several states would have to take this extraordinary step, a move that would cause extreme backlash and a real crisis of democracy throughout the country.

“There’s a strange fascination with various imagined dark scenarios, perhaps involving renegade state legislatures, but this is more dystopian fiction than anything likely to happen,” said Richard Pildes, a law professor at New York University. “The irony, or tragedy, is that we managed to conduct an extremely smooth election, with record turnout, under exceptionally difficult circumstances – and yet, a significant portion of the president’s supporters are now convinced that the process was flawed.”