He didn't run in the Democratic primary because while Democrats can be weird, Democratic voters, including the rest of the Kennedy family, tend to reject this kind of weird.
That's true, but only as of like a year ago. He was a Democrat for like 50 years. Doesn't make this (or him) any less reprehensible and bat-shit crazy. I, for one, am glad he changed to an independent party affiliation.
Well, when he was a private citizen he was free to identify with whatever party he chose. But once he starting putting forward his candidacy it became quite clear that his form of politics was not in line with the party in several important ways. So it’s not as if he was a normal democrat for that period and abruptly changed. His differences became clear as soon as he was subject to public scrutiny.
But I would agree that he’s more a part of the political left than the right.