This is a beta test. They are circulating an outright lie and they are going to see how it takes. If it pretty much goes unrefuted, then there will be no limit to the lies they can run with in campaign ads.
Notice that they don’t actually claim that Trump said it. They’re counting on people ASSUMING he said it, not having heard the debunking.
That’s how they get away from a libel suit.
My hope is that Milwaukee folks know it’s a lie and the billboards themselves are just a reminder that dems lie and they don’t care if their city is horrible.