A public opinion poll is a snapshot of a moment; a wipe-out election such as Tuesday’s midterms has roots that run deeper into history. The word “historic” is thrown around so much these days; it has been shorn of meaning. But make no mistake, what happened this week is historic. There has not been a governing party wipe-out on this scale in the US since the 1974 midterms – also known as the “Watergate election”. That’s more than half a century ago.