They can’t because of the 50-50 Senate. All Mitch has to do is repeat the Merrick Garland strategy and refuse to hold a vote. With Harris gone they can’t break the tie - nor force through any particular piece of legislation.
This, of course, would not prevent Romney, Murkowski, or any number of other faux conservatives from voting with the Democrats- but it creates risks Democrats don’t need to take.
What an interesting thought. Yes. That would definitely be a problem. Looks like he is stuck with her until the end of the term.