What happens if the Supreme Court didn’t become an election issue???
Polling at the time suggested the Supreme Court issue was polarizing in the sense that it attracted Republican voters who were wavering. If the seat did not come open, I think Nelson would have been reelected, and O'Rourke/Donnelly/McCaskill would've all found themselves in a better position (though I don't know that any would have won). Democrats might also have been somewhat stronger in the House.
The Supreme Court being a prominent topic of discussion close to the election was also helpful for the Republicans in 2020. As the conservative majority in the judiciary becomes more entrenched I expect this not to work so well in the future, but it was the issue that allowed the GOP to rally in both 2018 and 2020.
