There isn’t one. He has no proof of voter fraud outside of Twitter posts and supporters reeing about actually legal things. The only success he’s had is separating the late arriving ballots in PA. Those haven’t been counted yet either so if he throws those out he throws out his chance at winning the election. Trump cannot win without PA.
Trump declared victory before any of the mail in votes were counted. Anyone with half a brain can tell you that the mail ins would be very important this election and would take time to count. Normally, it takes a few days to count mail ins, but you can do statistical analysis on what percent of the vote remains to give you a good idea of what things look like. In a normal election year without a massive pandemic and politicizing of mail in votes, mail votes and absentee ballots tend to lean dem anyway. Trump made a huge fucking issue about mail in ballots because he needs something to blame if he’s losing (and it could never be that people just don’t like him, it has to be fraud) and demonized the hell out of them. More people voted by mail this year than ever before because of the pandemic. These votes already leaned democrat, but now they’re solidly so, as less trump voters took the option to mail in a ballot and instead went to the polls in person - that’s why Trump had such a big lead on election night. Wisconsin, Michigan, and Pennsylvania all have laws saying you can’t count mail in ballots until the polls open on Election Day - these laws were passed by Republican state legislatures. Trump even before the election was trying to throw out a large chunk of ballots in PA, so counting was going to be slow and careful. Again, normally not an issue but holy fuck there’s a lot of mail in voting this year, which means there’s a big delay in the results as everything has to be counted, confirmed legal, and they couldn’t get a head start on it.