This has to be illegal.
If a boss can't intimidate their employees this way ("A vote for Biden is a vote for a pay cut and layoffs!"), then there's no reason this should be allowed.
Why would it be illegal? A "boss" and an "employer" are two different sort of relationships.
Our kids' schoolteachers, through their unions, send parents all sorts of messages about how dire things will be if they vote wrongly. Our Doctors tell us how much more healthcare will cost if we vote wrongly. The landlord has free speech, does he not? Is he/she threatening tenants with eviction?
Elections have consequences. One consequence is greater or lesser tax consequences on voters, or on specific groups of voters. This is a cheesy appeal, but I find it hard to see how it's illegal.
Lots of things wrong with this post. First, unions endorse candidates all the time, but they're certainly in no position to yield threats, implied or otherwise, if an election doesn't go the way they want.
Second, I don't know what kind of doctors you've been seeing, but I've certainly never had one tell me how to vote and it would be totally unprofessional and unethical for a doctor to use their practice to shill for their preferred political candidates.
Thirdly, the way this particular landlord is behaving is pretty blatantly unprofessional (not new behavior from these kinds of folks, of course... and I just escaped an abusive landlord engaged in criminal behavior myself) and if they are using this as an implied threat, then that would be illegal. At a second glance, it looks like they're just trying to use whatever fear or intimidation tactics they can get away with. But the fact of the matter is that a person's vote cannot lawfully be tied to their employment or status as renters.
Now it is legal, of course, for the landlord to double the rent if Trump loses. But as Joe said, chances are they already anticipate that happening and are just looking for an excuse to grift from that loss in any way they can.
Which is also unethical, but then again, landlords aren't exactly the first thing to come to mind for most people when it comes to ethics, or professionalism, or basic human decency for that matter.