> the way that labor-oriented political parties are constituted and have their priorities decided in the US is backwards from those in Europe (top-down vs bottom-up)

I don't believe the proposition that parties in Europe have their priorities decided in a bottom-up manner. And the problem with having labor unions that are not-quite political parties is that you'll end up with unions which are concerned by issue far of from the concerns of the workers, which then tend to not suscribe