Glad the piece rang some bells for you too.

I liked the explanation for the rising importance of authenticity - the immediate backlash the internet allows for whenever there is a photo op that looks contrived or awkward, that exposes some intent to try to appear other than one is. You can't have answers that aren't second nature, that don't flow easily from your core values. Which means, like you say, that these heads of broad coalitions - so often stuck trying to juggle sensitivities of different wings of that coalition - often end up with their foot in their mouth. That was what made Sanders' job so much easier than Clinton's. She was in a bind trying not to upset corporate donors while trying to empathize with anti-corporate left-wingers. Trying and failing to thread that needle leaves you worse off because you get labeled as fake and untrustworthy. That said, somehow Obama managed in '08 to thread that needle by just lying straight-faced in public and reassuring donors in private (notably on NAFTA, most likely on banks and health care too). The lying worked, but along with an ability, when it mattered, to address the hard questions with candor like the post-Reverend Wright speech. A shocking faith that the public could be treated like adults. That gets you brownie points. 

On the length of campaigns? Not sure I agree. With a shorter campaign season it is doubtful that Obama would have gotten anywhere. Same is true of Sanders. Nobody can say that they didn't know what they were getting with Trump. Short campaigns in the UK are fine because candidates have time to literally go out and meet half the country. Corbyn has managed an impressive surge despite a wall of negative across the board media coverage (the Guardian and the BBC as harsh as the right-wing tabloids). Sanders managed a slow climb thanks to campaign events and would have never gotten off the ground without the luxury of time to build. Social media has allowed these outsiders to spread their message bypassing media blackouts, but it hasn't radically shortened the time required to raise one's profile significantly. 

On other reasons for the rise of authenticity, I always think back on the very different worlds my generation X and this millennial generation have grown up with. You allude to some things - the self-conscious social media branding for instance. Which is important. But it goes deeper than that. In this context I often think of David Foster Wallace's overly long and wandering piece on the TV generation, about how TV engendered passivity and a self-aware brazening out of that helplessness through irony. The information, the programming, the framing was fed to us, we had the option of maybe turning that vehicle of elite messaging on or off, but control was in effect out of our hands. It provided the comfort of knowing what to think, that there was a consensus; what does Cronkite say about so-and-so?

But there was also an implied impotence. The kind of empowerment that arose for the Children of The Web, led not just to a democratization of geek-culture, dropping the barriers to entry to any field of esoteric interest, but to a powerful and general assumed independence: what do you want to know today? - is what the Google home-screen says. It's literally a blank screen asking for your command. There is no longer an imposed message about what to think and about what things to think at all. Self-curated journeys of curiosity become the norm. It makes for a generation with much less patience for bullshit, for the kind of top-down messaging that says "this is just how things work, just trust us, the elite". Trying to narrow down the domain of the possible for the electorate doesn't go down well. Older voters were fine with that subtext to Clinton's campaign for instance. Younger voters just found it bizarre. Self-curated information flows like that of the twitter barbers are just the surface manifestation of a deeper change in how their minds work.