First Avenue fires new general manager for supporting Trump

[SWE]

As long as he didn’t make his political beliefs a blatant and obnoxious part of his management style

That type of position is public facing so the way you interact with the world on social media is a part of your job description.

He did it long before actually working at the company, this should have no bearing on his employment. It would be different if he continued to engage in blatant political messaging while acting as the public face of the company.

1) not "long before"
2) evidence of this substantial character flaw was available before he started the job, not necessitating finding out during the course of his employment

His feed was inactive for two years before he was hired; I would hardly consider that recent. If it wasn’t for social media the people who did this digging on him wouldn’t know anything about his beliefs. I’ve worked with people whose beliefs I don’t always agree with, but I don’t raise a stink about it because at the end of the day it usually has little impact on me. Judging people entirely by their political beliefs is pretty toxic and shouldn’t have any bearing on someone’s employment status if they keep it out of the workplace.

Not sure what it's going to take for this to penetrate the outer membranes of your skull, but again: he was not fired for his political beliefs, he was fired for making offensive public statements inconsistent with the mission of his employer. Maybe he should have deleted them if he no longer agreed with them or better still never made them in the first place. Don't like at-will employment? Move to France and find somebody who cares.

Republicans in this thread are really melting down at the consequences of their own votes (for politicians who support at-will employment)

Well republican politicians could add private political speech to the CRA if they wanted to protect their own voters

Such a provision would never get passed SCOTUS

[Ferguson97]

Religion is a protected class as well, and it can be argued that Evangelical Christians and conservative Catholics are "disfavored" groups. 

No, it could not be argued that. They are the dominant religious groups in America in terms of political and legal power.