You omitted one key word in your post -- "Independents." We're out there. Lots of us. And we sway elections. Many wouldn't approve of court-packing, and if Democrats win and go that route, they'd better pass stuff quickly, because they'd likely get squashed in the midterms. This election absolutely is a referendum on Trump. The 2022 midterms will be a referendum on Biden/Harris.
As for the Tea Party: To me, they're the "Squad" Democrats. Their beliefs are not representative of most Americans', and they're mostly looking to pick a fight -- even if it's with their own side. If Biden wins -- heck, even if the Democrats take the Senate, too -- it won't be smooth sailing. The radicals in the party will try to move Biden far left, and if he does that -- full circle -- he pi$$es off many Independents. Unfortunately, that's politics on both sides, and that's why Americans consistently lose, regardless of who "wins."