Since the Tea Party is not an official political party, doesn’t run candidates under it’s own name, I can see allowing the shirt. A person could wear an SEIU shirt for the same reason.
I will admit though, Christians don’t run candidates under the Christian party either.
The problem may be as simple as this.
“Vote for...”
Wear a shirt saying “I love Jesus” for instance, probably wouldn’t be a problem. “Vote Jesus”, probably would be.
Vote SEIU, or vote Tea Party, probably would be a problem.
The article was about “Vote the Bible”, which as far as I can tell is not a candidate or political party, therefore should be allowed, right?