Fire their asses.
The conditions of employment are set by the employer, if they find these conditions too difficult, for example the requirement to act like mature adults instead of foolish asses while on duty, they can find work elsewhere.
Their political views are NOT germane to their job. It would be the same as if I stood up in the middle of a corp meeting and started blabbing about Free Republic to everyone.
A few years ago I had to fire an engineer who had nothing but political agendas. Straightaway he tried taking over operations (I was the boss BTW), and going into far left political rants, with the phrase “effing American b@st@rds” thrown in frequently (he was U.S. born). I fired him in short order. I didn’t care how much “experience” he had.