It's a free country and a guy made a decision regarding what he was willing to have HIS company say publicly. It was his call to make. His company. Privately funded. He's got the right to run it any way he sees fit. You have the right to cancel subscriptions and decline to read it. Advertisers have the right to flee. Everyone has a choice. Thats how this whole America thing works.
Besides, who was making their decision based on the Washington Post's editorial board endorsement anyhow?