Hillary Clinton continues to hold a small lead in FiveThirtyEight’s forecasting models. She has about a 59 percent chance of winning the election according to both our polls-only and polls-plus forecasts. The most notable new polls released since Friday came in Pennsylvania and Florida, both crucial swing states. Clinton led by 8 percentage points in a Muhlenberg College poll from Pennsylvania and by 1 percentage point in a Siena College poll out of Florida.

How crucial are Pennsylvania and Florida? They’re more crucial than all the other states. But they’re still not that crucial. You often hear that some battleground state is absolutely key for Clinton or a must-win for Donald Trump, but really no single state is that pivotal. The map is pretty fluid.

You can see this best in our tipping-point state calculations, which show each state’s chances of providing the decisive 270th vote in the Electoral College for the winner. Here are the current rankings, according to the polls-only forecast :

STATE CHANCE OF BEING TIPPING POINT Florida 15.9% – Pennsylvania 10.9 – Michigan 10.7 – Ohio 10.4 – North Carolina 9.0 – Colorado 6.1 – Virginia 5.8 – Wisconsin 4.9 – Nevada 3.6 – Minnesota 3.1 – New Hampshire 2.3 – Iowa 1.8 – New Mexico 1.6 – Maine 0.6 – There is no ultimate swing state FiveThirtyEight polls-only forecast as of Sept. 19

Notice that Florida is the most pivotal, but it’s only the tipping-point state 16 percent of the time. After Florida, there’s a big drop-off to Pennsylvania, Michigan and Ohio, which each prove decisive in about 11 percent of our simulations.

There are, however, states that Clinton or Trump win in the vast majority of cases in which they win the election, according to our model’s simulations. But that’s not quite the same thing as a must-win state. Trump has to win Arkansas, for example, but not because Arkansas’s six electoral votes are so valuable. Instead, if Trump is losing in ruby-red Arkansas, he’s likely losing in most other states. The states aren’t independent. So the truly “must-win” states tend to be the noncompetitive ones, and they don’t guarantee Trump or Clinton a win — they simply preclude a loss (most likely).

Among the swing states, there are particular ones that Trump and Clinton need to avoid losing. If their opponent is ahead there, it’s an almost a sure sign to the candidates that they’re losing the election: For Trump, these are the light-red states (e.g., Ohio, Florida and Iowa); for Clinton, they are the light-blue states (Pennsylvania, Michigan, Minnesota and Virginia).

IA OH FL NC NV NH CO MI WI PA VA MN ME NM Clinton’s chances if she wins state 95 95 94 91 87 82 82 80 80 79 75 75 74 70 Clinton’s chances if she loses state 39 33 28 34 32 21 18 9 10 13 12 10 19 20 Trump’s chances if he wins state 61 67 72 66 68 79 82 91 90 87 88 90 81 82 Trump’s chances if he loses state 5 5 6 9 13 18 18 20 20 21 25 25 26 30 Clinton and Trump have different ‘must-win’ states All values are percentages. FiveThirtyEight polls-only forecast as of Sept. 19.

A Clinton win in Florida would be a very bad sign for Trump. In 29 percent of our polls-only model’s simulations, Clinton wins the election while losing Florida; Trump wins just 6 percent of the time when losing the Sunshine State. It’s as close to a must-win for Trump as a battleground state can be (although, again, the causality is backward — Trump doesn’t lose the election because he loses Florida, he loses Florida because he’s losing the election). Florida leans slightly more Republican than the country overall, so a GOP candidate almost always wins it when winning nationally. The last time a Republican won the presidency without Florida was in 1924. Trump is just the slightest of favorites in Florida at the moment, with a 52 percent chance of winning the state — which gives you an idea of why he’s still an underdog in this election.

Other nearly must-wins for Trump include Iowa, North Carolina and Ohio. Trump holds small leads in all three states but has less than a 60 percent chance in North Carolina and Ohio. Now, it’s not as if Clinton doesn’t want to carry these states. She wins only about a third of the time when she doesn’t, but she doesn’t need them like Trump does.

Pennsylvania, on the other hand, is close to a must-win for Clinton. She wins only 13 percent of the time when she loses that state. Trump wins a slightly higher 21 percent of the time without it.

Two other states that Clinton pretty much needs to win are Virginia and Wisconsin. Virginia lined up nearly perfectly with the national vote in 2012 but has continued to move left since then, and Clinton rarely wins without it. That might explain why Trump has spent a lot of money advertising in the state even as Clinton continues to lead there. Wisconsin is a different story. It has gone Democratic in every election since 1988, but Trump is hoping whites without a college degree help him turn the state red. He has not led in a single high-quality poll in the state but did close the gap in a recent Marquette University poll.

There are more idiosyncratic states, such as New Mexico and Maine, which have leaned solidly blue in recent election but which tend to move more independently than other states. Losing in Pennsylvania is bad for Clinton because she loses the state’s 20 electoral votes, but it’s also bad because there are a lot of states that tend to vote similarly to Pennsylvania. That’s why it’s better to look at the map as a whole, rather than looking for a single keystone state.





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