Florida is the key state

Whoever wins Florida is likely to become the next president.  Florida has 29 electoral votes and counts its vote quickly, so we are likely to know the winner of Florida by midnight on election day and thus who the next president will be.  By the way, Biden has a 70% chance of winning Florida, so we can state that he has a 70% chance of being the next president.

I am playing around with the  270ToWin map, and also the FiveThirtyEight map, and this is what happens to the winner of Florida.  

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1. If Biden wins Florida, then he is the next President.  He will have at least 319 electoral votes and there is no way Trump can win.

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2. If Trump wins Florida, then the pathway isn't as clear but it sets off a chain reaction that results in a Trump victory.  The first chain is that other states that are highly correlated with Florida will also go for Trump. These states are Georgia, Iowa and Ohio.  The next chain is that two states that are leaning Biden will go for Trump because of correlation - Arizona and North Carolina.  Also Maine's 2nd District.  Now stop at this point - it looks like Biden has 279 electoral votes and Trump has 259.

But see what happens when probabilities become certainties. Let's choose the winner of each state in this order:  1. Georgia, 2. Iowa, 3. Ohio, 4. North Carolina, 5. Arizona.

At this point, Trump has an 81% chance of getting Maine's 2nd Congressional District so lets give that to him.  Now Trump has a 69% chance of winning Nebraska's 2nd District so give that to him. At this point Trump has a 75% chance of winning Pennsylvania and a 72% chance of winning Wisconsin, so Trump wins.

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3. The Nebraska 2nd District seems to be another tipping point, so see what happens if Trump wins Florida but we don't know the winner in NE2.  Go through the first 6 steps above.  At this point, Trump has a 63% chance of winning Pennsylvania, 60% chance of Wisconsin, and 53% chance in Nevada. 538 predicts Trump's overall odds at this point are 77%.  If Trump wins either Pennsylvania or Wisconsin, he has it.  

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4. What is the most likely scenario if Trump wins Florida, and then Georgia, Iowa and Ohio?  Well, he will probably win North Carolina, Arizona and ME-2, but that isn't enough.  It looks like Biden 279 to Trump 259.  So Trump needs just a little more magic besides Florida.  And that is most likely to happen in Pennsylvania.  Trump's best case scenario involves winning these two states.

So let's recalculate.  Trump has a 30% chance of winning Florida and a 13% chance of winning Pennsylvania, calculated separately.  If Trump wins Florida, his chance of winning Pennsylvania jumps to 35%.  Multiply 30% by 35% and you get about a 10% chance of Trump winning.  So I understand Nate Silver's math a little better.

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On the other hand, you could say that Trump has a 30% chance of  Florida, and this would give him a 77% chance of winning under the 3rd scenario.  So this would make Trump's odds 23%.  This makes sense to me, so I will say that as of now, Trump has a 23% chance of winning.