As for closed shop:
https://en.wikipedia.org/wiki/Union_shop#United_States
It's illegal, so's the similar "union shop", and you can opt out such that you still pay dues but they may only go toward collective bargaining activities and services to members, which appears to solve this "I'm being forced to support the only viable political party that wants to make anything whatsoever better" problem. Maybe leaving others, sure, but this issue's... not an issue. Unlike employers. I can't sign a piece of paper banning them from using profit derived from my labor for political activity.