… The reason is that our forecast models use both state and national polls to estimate where the national race stands. In fact, they put most of the emphasis on the state numbers. Historically, it’s been more accurate to take a “bottom-up” approach — first, forecast the vote in each state, then sum the numbers together — than to force everything to match the national numbers. …
So that means Clinton’s swing-state numbers must be really good, right? They’re pretty good — but not great, although she’s gotten some better numbers in the past week. Instead, her biggest comparative strength — and Trump’s biggest comparative weakness — comes from red states rather than swing states. CONT.
Nate Silver, FiveThirtyEight