Perhaps you have missed the point?
If indeed Tunney was the inspiration for McKay in 'The Candidate' (and if this was a fair and reasonable depiction of him - which as I understand it, it was), wouldn't you say that his absence from future politics was a good thing? I mean, McKay was an empty suit, with no real ideas of his own, utterly manipulated by an unscrupulous campaign manager. Such a man, someone with no real executive experience or understanding of the world outside of his own bubble being elevated by shadowy outside forces to the presidency....
Oh, wait.... nevermind...