Data Science

[timelets]

The data is certainly noisy, but an emphatic win on the order of what Clinton or Romney achieved — and perhaps what Hillary Clinton achieved on Monday night — might be expected to produce a swing of 2 to 4 percentage points in horse-race polls. Even a 2-point gain would do wonders for Clinton, who would go from a fairly uncomfortable position in the Electoral College to a fairly comfortable one, and who would emerge with a 3-to-4-point lead in the popular vote.
http://fivethirtyeight.com/features/clinton-won-the-debate-which-means-shes-likely-to-gain-in-the-polls/

Trump is a poor debater; he's simply not skilled in a fair competition format.