The statements about his liberalism are not yet documented. If contributors assert things, it is their responsibility to document it. I would say that his musical accomplishments in the US and the rest of the world far overwhelm the importance of any one political commercial for or against anybody. There were even conservatives who had anti-Reagan commercials at one point or another. It was his astounding talent and charisma that propelled him to fame, not the fact the he was a liberal.
When you begin a sentence with "perhaps", you can write just about anything.