Let me chime in on PIPs with some pearls of wisdom, for whtever they're worth.
If you get put on a PIP, first thing I would do is get very clear on what they actually want from you, and I mean VERY clear. Dont accept the usual vague stuff like "needs to demonstrate leadership" or "needs to communicate more effectively." Ask what specifically you're supposed to do differently, how they're measuring it, and what passing the PIP actually looks like. Then write stuff down and I don't mean start acting like youre building a court case and copying half of EM on every email, that's probably going to make things worse. Just keep a record. If you meet with your boss and he tells you that you need to do X by Friday, send him a normal email afterward saying thanks for meeting, just wanted to make sure I understood, I'll have X done by Friday and we'll review Y next week.... Because 2 mo later memories have a funny way of changing. Same thing if they say you didn't do something and you know you did. Don't get into a big fight about it, just correct it. "I think there may be some confusion here, I sent that on the 12 th, see attached." Keep it factual and keep your emotions out of email, which is probably harder than it sounds when you're pi---d off and worried about losing your job. Also pay attention if the requirements start changing. If they told you one thing at the beginning and suddenly you're being judged on something else halfway through, ask about it. Again, don't send some crazy email accusing everyone of moving the goalposts. Just ask, "I thought the expectation we agreed on was X. Has that changed?" Now it's documented and u good... I also wouldn't run to HR expecting them to straighten everything out because your mgr is being unfair. HR works for the company, protect EM is the mission... Sometimes they can help especially if something doesn't smell right, but they're not your personal advocate. Just understand that going in.
Here's another thing people don't like hearing... Maybe the PIP is bullsh-t (I kinda think it is)... But maybe it isn't. Find somebody you trust who knows your work and ask them, and don't pick the person who's automatically going to tell you your boss is an a--hole. Find somebody who will tell you if YOU are the problem. That's useful information too. If you honestly think there's discrimination, retaliation, protected leave or something legal involved, then I'd talk to an employment attorney. That's way beyond anything you're going to figure out from this board. And personally, the day I got a PIP would also be the day I started looking for another job. Not because you're definitely getting fired. People do survive PIPs. But at that point EM has formally told you there's a problem with your performance and you'd be nuts not to prepare for the possibility that this doesn't end well.
So I'd work my a-s off trying to pass it while at the same time quietly working on getting out. And don't quit just because you're angry. Don't send the email you really want to send. Don't tell your boss what everybody thinks of him. Don't make some grand stand on principle. Be boring. Do the work, ask questions, keep notes, save the emails. If they say you sc--wed something up and you didn't, correct the record. If they change what they want, ask why. Meanwhile get the resume out there. Best case, you pass the PIP and now you have choices. Worst case, at least you didn't spend PIP period assuming everything would somehow work itself out.