Here’s a good question by Jen McGregor on p. G2, “Taking Stock”, of the Washington Post on Sunday June 4, 2017, “Off-hours activism can hurt you at work” (?)
She notes that about 12 states have laws prohibiting private employers from interfering with off-the job activity unless it involves trade secrets or privacy issues. Attorney Gene Volokh says that this problem doesn’t come up as often in practice as one would expect, because most employers find a “live and let live” approach better for business.
However, there can be a hostile workplace issue when people with direct reports engage in some open speech off the job, as I outlined here or here on my legacy site.
I would wonder how this plays out in Trump's businesses.