Most of Trump's legal challenges appear pretty spurious, but there's one that people need to keep an eye on. It relates to mail-in ballots received up to 3 days after election day in Pennsylvania. (Thread)

Election rules are set by State law, so accepting late ballots is fine if the State law says so. However, in PA, the rule derives not from State legislation, but from a State Supreme Court decision. This is what the Republicans are challenging: they say this is not legitimate.

The Supreme Court has already twice declined to review this case for different reasons. However, in doing so, Alito J stated his view that there is a "strong likelihood that the State Supreme Court decision violates the Federal Constitution." https://www.cnn.com/2020/10/28/politics/supreme-court-pennsylvania-mail-in-deadline-barrett/index.html

Last night, Alito J ordered that the late ballots be separated, so that they can be discounted in the event that a later decision disqualifies them.

This indicates that the US Supreme Court may well be open to disqualifying these ballots. So to be safe, Biden either needs to win PA by more than the number of disquslified ballots; or win the Electoral College without needing PA. (It seems possible/likely he will do both.)