Trump’s legal challenge is going to be directed primarily at mail-in ballots, the largest source of fraud in this election.
They will argue that:
1) the mail-in ballots and the extension of the voting deadlines violated state law, since they changed election law, bypassing the state legislature.
2) Republican observers were barred from the counting rooms in violation of state law.
3) the casting of illegal ballots cancels the legal ballot of voters, which is a civil rights violation.
4) treating the ballots in these Democrat controlled cities differently than the rest of the state is an equal protection violation.
This will be pressed on all fronts to get many, or possibly all, of the mail-in ballots thrown out in the states where these violations occurred, if not nationwide.