Voter registration records are a public record, but there's slightly different practices and administrative process fees from state to state. Voting record data is large, and I've worked with it on about half the states. There are aggregation services that take the trouble of keeping up with all 50 states' rules and fees, but then you certainly pay them for the service. It's pocket change when you are talking soros money. In many cases there is information of which party you registered as, and there's frequently historical records going back some X years on how you registered. So if you register as a republican (in such states where they have closed primaries or party registration), then it's at least safe to say that they would want to throw out your ballot.  It works in their favor. If you (R) voted for Biden, then they replace your vote 1:1. If you (R) voted for Trump, then throwing out your vote subtracts a vote that Trump would have gotten and gives it to Biden.