“It allowed extensive prior use of political clothing in prior months and years, both for this and other employees.”
If true, they set a precedent and could be SOL on this one. They can announce that from this day forward, the policy will be enforced, but this guy should be safe considering the precedent.
They did and gave him plenty of opportunities to remove his hat, but he refused.
He was being insubordinate and his hard-headedness cost him his job. Doubt he'll find someone to take his case unless he can demonstrate that people are currently wearing Biden/Harris ball caps to work without censure.