With nine days left, massive polling error is Donald Trump's best shot to win

He has run out of time to truly turn things around

There are two major sources of error in handicapping the election. The first is the chance that the electoral environment changes between whatever day you’re making the forecast and election day. The second is the chance that the polls are so systematically biased toward one candidate that the other one pulls off a surprise victory (see: 2016).

With only nine days left in the election, Donald Trump has lost the majority of the cushion that the first time of error offered him.

Let me explain a bit more. Election forecasts work by exploring a range of potential scenarios for what the future might bring. Hence the forecast. You can think of those futures as getting less predictable over time, forming a cone of potential increases or decreases in a candidate’s share.

Over the last 6 election cycles, the margin of error on the movement in a Democratic presidential candidate’s polling margin from 300 days out to election day has been roughly 20 percentage points. We can also define that margi…