No! Don't think about The Turtle! Look everybody! The libs are old and senile too! LOOK! [please don't look at the turtle. Nothing to see here. Nope The Turtle is fine. Look! It's a sleepy old person who is a democrat!!!]
It's true, but in Mitch's case it might be that staying literally kills him. He's the minority leader in the Senate, which has got to be stressful, and if the fugue state he entered was caused by a mini-stroke, he needs to be resting and avoiding stress like a literal plague.
She’s already said she won’t run at the next election.
But if she steps down now, the republicans can refuse to let a new democrat sit on the judiciary committee (that she’s on), then the Republicans can just deadlock the vote to appoint any new federal judges (exactly like they did when she was on sick leave).
The US political system is broken, but Feinstein is doing the best thing she can for her party and the people who voted for her.
Appointing a new committee member would require unanimous consent. Generally that’s easy - it’s a procedural step and the party in majority will ultimately get their way, so senators all give consent so they can get back to doing some actual work on the senate floor. But some first-term far-right republicans are withholding unanimous consent now, forcing the senate to decide if they want to waste days debating so they can vote, or just move on to something else.
Eg, Senior military promotions require senate approval, and it’s typically a matter dealt with in a few minutes because the promotions are given unanimous consent. Senator Tuberville is a first-term MAGA Republican and an anti-abortion zealot. For months now, he has been blocking military promotions, demanding that the pentagon reverse their decision to allow service members to travel out-of-state if they require reproductive healthcare. Even if the other 99 senators approve of the promotions, to take a vote they would need to table it, go to committee, debate it, avoid a filibuster, and ultimately vote on it. So a task that should take minutes can instead turn up the senate for days or weeks, preventing the senate from getting anything else done in that time.