 In this particular case, Trump is a 66% favorite. That doesn't mean for sure he's going to win. Remember that all the models had Hillary Clinton, like a 99% favorite in 2016, and then she lost. With that said, he says if Biden loses Georgia, Arizona, and Nevada, he needs to win all three of Michigan, Wisconsin, and Pennsylvania, not just one of them. Even though these states are pretty heavily correlated, they aren't perfectly correlated. Winning several different correlated bets is still hard. These states have significant differences.