The GOP will have 54 senate seats assuming the most likely remaining scenario that Tester wins Montana, Scott wins the recount in Florida, and McSally takes Arizona. Let's look at 2020: the Democrats will almost certainly lose Doug Jones' seat in 2020. So that puts them at -8. They'll probably be able to pick up Gardner's seat in Colorado, so they're -6. The only other two flips that really look possible are Ernst in Iowa and Tillis in North Carolina. So let's go best case and assume they get both. Now they're -2. So these losses last night were absolutely devastating, especially Florida and Indiana which were polling well for Democrats.
Even if the Democrats win the presidency in 2020 the GOP will control the senate and thus will block any supreme court nominations. And the Democrats winning the 2020 presidency looks really shaky right now. Last night's election should scare the out of Democrat voters. Even in an election with high enthusiasm Trump was able to turn his base out in enough numbers to again outperform the polls pretty strongly. Nelson, Donnelly, Sinema, McCaskill were all favorites yesterday morning and they're all losers this morning. Trump is going to be really hard to beat in 2020, especially if the Democrats nominate someone like Booker, Harris, Newsom, Klobuchar, or Warren that won't excite the base. I think it's Beto or Bernie or bust in 2020 because Beto and Bernie are the only people who can get young people excited and to the polls like Obama did.