I don’t think this is what the authors had in mind, but what I took from that dubious McCain story is that McCain has surrogates who care very much about his reputation and will intercede if there is even the appearance of impropriety or self-sabotaging behavior. What’s more, McCain appears to listen to these surrogates and the problem effectively gets dealt with.
This is in direct contrast to some important politicians in living memory — the Harriet Miers episode is illustrative here. And I get the distinct feeling that everytime one of Clinton’s liegemen should have piped up and said “Uh, Bill? Are you sure want to do that?” there was nothing but the sound of crickets chirping.