Idiot.
The First Amendment prohibits the government from censoring what you might want to say before you say it.
It does NOT make you immune to suffering consequences for what you’ve said after you’ve said it. If it did, we wouldn’t have libel and slander laws.
As a retired university professor, it is well known in academe that you can generally say what you want on social media but if you embarrass your employer, you will be fired. Tenure might slow the process but isn't necessarily protection from losing your position.