In the aftermath of the 2016 US presidential election, and the first few months of the Trump presidency, it is worth remembering the certainty with which most media outlets believed the 45th US President would be Hillary Clinton. Twelve months out, the winning candidate had a five per-cent chance of winning; at its last update, FiveThirtyEight's Election Forecast still put Clinton's chances of winning at 71.4%.
But this election was different from what had gone before. In 2008, Obama had seemed to be the forward-facing, progressive, internet-friendly candidate. He used Twitter and Facebook (or rather, his campaign did);...