As I noted over the course of 2016, if the polls had been off in 2012 in the Republican’s favor as much as they were off in Obama’s favor, Romney would have been elected president. It shouldn’t have been a huge surprise when that actually happened this year. Sometimes polls are a little more favorable to toward Democrats, while other times they are more favorable toward Republicans.
What occurred wasn’t a failure of the polls. As with Brexit, it was a failure of punditry. Pundits saw Clinton with a 1.9 percent lead in Pennsylvania and assumed she would win. The correct interpretation was that, if Clinton’s actual vote share were just one point lower and Trump’s just one point higher, Trump would be tied or even a bit ahead.
Instead, people gravitated toward unreliable approaches such as reading the tea leaves on early voting or putting faith in Big Blue Walls, while ignoring things like the high number of undecided voters. They selected these data points rather than other possible indicators, such as the significant late break in the generic ballot that could have led them in a different direction. To be blunt, people saw what they wanted to see, and then found the data to support that view.