Nate Silver writes at Five Thirty Eight,
Here at FiveThirtyEight, our favorite election-related chart is what we officially call the “winding path to 270 electoral votes” and unofficially call the snake. Designed by my colleague Aaron Bycoffe, it lines the states up from most favorable for Hillary Clinton (Hawaii, Maryland) to best for Donald Trump (Wyoming, Alabama) based on the projected margin of victory in each one. The snake is bisected by a line indicating 269 electoral votes: cross this line — meaning you get 270 electoral votes — and you win the election.
Right now, Clinton is over the line by exactly one state. As of this writing, that state — what we also call the tipping-point state — is New Hampshire. But a group of states are closely lumped together, and Pennsylvania, Colorado and Wisconsin have all taken their turn as the tipping-point state in recent weeks.
If she wins all those states and everything toward the blue end of the snake, Clinton would finish with 272 electoral votes, even assuming she loses the 2nd Congressional District of Maine. (Maine and Nebraska split their electoral votes by congressional district.) That’s two more than she needs to win the election.
But in different ways, that both understates and overstates how precarious Clinton’s position is. It understates it because Clinton has no margin to spare. Clinton’s polling has been somewhere between middling and awful in most of the other swing states lately, and they all at least lean toward Trump at the moment, narrowly in some cases (such as Florida) and more clearly in others (such as Iowa). If Clinton loses any of the states on the blue side of the snake without picking anything up on the red side, she’ll be stuck on 269 electoral votes or fewer.
On the other hand, Clinton’s leads in the states she needs to win appear to be pretty solid. As of late Thursday afternoon, she’s ahead in our forecast by 3.1 percentage points in New Hampshire, and by slightly more than that in Colorado (3.3 points), Pennsylvania (3.4 points) and Michigan (also 3.4 points).
…State polling averages have been pretty good for the past few presidential elections, but “pretty good” still provides for plenty of times when they miss by 2 to 4 percentage points. If one of those misses is in Trump’s favor in Pennsylvania or New Hampshire or Colorado, especially if the race shifts a bit further to Trump overall, then Clinton will go from being in a pretty good Electoral College position to having a total mess on her hands.
…how safe can Clinton feel in Colorado given her poor polling in Nevada? Can she be entirely comfortable in New Hampshire given that Maine is surprisingly close? Does the sharp tilt toward Trump in Iowa tell us that Wisconsin or Minnesota have the potential to turn red?
Read more here.