1. People who voted for trump initially voted for him despite the fact the man could have led us into nuclear holocaust. Now we know Trump won't do that, and he has run a presidency without doing anything disastrous (that these voters care about) so they're more assured of their vote. I imagine a lot of people on the fence fell for Trump the past 4 years. 2. Everyone who wants Trump out is more motivated than 2016, so literally anyone who can vote is doing so. In 2016 trump was the joke vote so he wasn't taken seriously. Now lots more liberals are activated.