From the Guardian:
Election experts are deeply worried about the chaos from a scenario in which Trump leads in-person voting on election night, claims victory, only to see his lead evaporate as more mail-in votes are counted. Election law experts are already warning that the 19th-century law that would guide how a disputed electoral college vote is decided is incredibly vague, and could lead to chaos as well as further high-stakes legal fighting in the courts.
“If it’s close and the courts get drawn in on potentially decisive issues, Bush v Gore will look like a walk in the park compared to what [this] would be like,” said Richard Pildes, a professor at NYU Law School who studies election law. “Social media and cable television will inflame with sinister spin any problems in the process, no matter how legitimate or normal those problems might be; many on both sides are primed already to believe the election is being stolen if their candidate loses.”