There's just not really any other explanation for how destructive he is, and how obstinate he is when he is outright destructive -- how nonchalant he is in the face or utter moronacy. I'm not defending him by saying many of his most dramatic actions are at gunpoint - I think he's a poisonous person totally separate from being someone's puppet. But I do think somebody owns him. There is an incongruence that isn't fully explained by shear lack of principle.
We all think he's sold out his principles, but usually that's just an expression. I think he literally has. Still, I'd accept the notion that he really is just a not-good-person. I think both may be true.
No, no I don’t think the left has “more” blackmail on McCain - other than the facts we already know (5-time USN pilot crashes and plane losses, POW turncoat, reckless and womanizer, Keating Five bribes, etc.) What HE has is the immediate and constant ABCNNBCBS TV exposure that he thrives on and lives for. As long as McCain will fight Trump (or conservatives) HE will be sainted and kept in front of the TV cameras.
And THAT McCain lives for.