He was still wrong though. The ban isn't on anything that might seem vaguely political... gay pride flag, blue line flag, trans flag, UAW hat, etc.

They just can't support a candidate or political party.

It depends. In Minnesota, wearing any of the items you listed would be considered electioneering if that was a major issue of the campaign.

So if one candidate has made gay rights a major plank of their platform, then wearing a shirt with a gay pride flag would run afoul of the rules. But that same shirt would be allowed in the absence of that specific issue being promoted by a candidate’s campaign.

That means the rule would be wide open to interpretation. After all, who decides what a major issue is?

It would seem far easier, and straightforward, and not a burden on anyone is simply wearing a plain shirt.

I'm fine drawing a line for an officer carrying out election duties that goes further than for other people.

They just shouldn't wear anything that puts the election workers in a position where they have to evaluate the political message. I guess that can be tricky if a uniform somehow became partisan though.

Being a policeman is becoming a partisan issue in itself, I guess

That framing is very generous to the status quo.

There likely is a moderately sized group of people who are opposed to having police, but the real partisan divide is over what sort of policing is acceptable, not over policing itself.

And even that is not really a sufficient explanation of the differences in opinion, it's too simplistic. People disagree about whether police are biased and things like that.