They would be changing jerseys tout suite, and the press would deem them a hateful, racist, bigoted xenophobic (etc, etc) monster until they had no support left from anyone.
The press reaction is very predictable. But I think the reaction of the people would probably not be as predictable as we think. That might be a most welcome and uplifting message to the very people who have heard nothing but “special interest” pandering for decades.
It would an interesting experiment, to say the least.