Harry Enten: “Even at the end of a presidential campaign, polls don’t perfectly predict the final margin in the election. Sometimes the final polls are quite accurate. An average of national polls in the week before the 2008 election had Barack Obama winning by 7.6 percentage points. He won by 7.3 points. Sometimes, however, the polls miss by more. Four years ago, an average of survey results the week before the election had Obama winning by 1.2 percentage points. He actually beat Mitt Romney by 3.9 points.”
“If that 2.7-point error doesn’t sound like very much to you, well, it’s very close to what Donald Trump needs to overtake Hillary Clinton in the popular vote. She leads by 3.3 points in our polls-only forecast.”
