As long as he doesn't tie continued employment to how people vote and isn't actually pressuring people or persistently asking them how they plan to vote it's annoying, but I don't think it's illegal.
It is inappropriate, but I don't think telling people his opinion, the way it was phrased it is illegal.
But if the boss has a boss, THAT person should be told, because he is not supposed to use company resources for political campaigning.
Except, in this case, the individual was on the Board of Directors. The only "boss" Directors have is a majority vote against them by other Directors.
You put it best, I think.