For those outside the US, and probably not a few inside, the US electoral college might seem an unusual system – why not just let the candidate with the most votes win the election? The reason, simplified, is to avoid people in densely populated areas dominating those in rural areas by weighting them differently. Understanding where to play, therefore, becomes essential in winning or predicting the outcome of the presidential election. In two of the last five elections, the winner of the presidency was not the candidate with the most votes. This means that even if I told you today the exact number of votes each candidate will get in 2020, you still wouldn’t know who the winner is.

This article examines the idea of flipping a state, so that a state that gave votes to your opponent’s party in the last election will give them to your party this time. In simple terms, each state works as a first past the post election, so if you take 48% of the vote versus an opponent’s 46%, you get all the votes from that state (usually). If you want to understand the details of how the electoral college works further, I recommend watching this video and those related to it examining some of its flaws.

Now let’s say you have been nominated the democratic candidate for 2020/ chosen as Trump’s key re-election advisor, and you are only allowed to visit 5 states, how would you decide which ones are your best bet for winning? First, let’s simply examine which states are ‘flippable’ and which rarely change their mind. For the sake of argument, I’ve started with the 1992 election (this is arbitrary as a start date, but the 1988 election was so overwhelming that it is almost misleading to use its figures), and looked at the 6 elections since. If a state switched party every time, it would get a flip score of 6, if it’s been constant for either party, it gets a 0 score. Our flip map since 1992 therefore looks like this:

This immediately makes our electoral strategy focus much sharper. Since 1992, twenty-nine of the fifty states have not once switched their allegiance, and while you can’t take anything for granted, there’s no logic in focusing on one of those over states like Florida, which has flipped 4 times since 1992.

Now this doesn’t show an accurate picture if we’re looking only to predict what will happen in 2020. Take for example Missouri, Arkansas and Louisiana: all three states voted Democrat in ’92 and ’96, but all have been fully Republican in the five subsequent elections. In 2016, Trump beat Clinton by more than 20 points in each of the three states, so it would be pretty reasonable to assume that they won’t be swing states in contention in 2020. So let’s pull the time-frame in a little closer, this time starting in 2004, so giving each state a maximum flip score of three.

At this point, we’re down to only twelve states out of fifty that seem to be worth examining for our strategy for 2020. And if we do a single step more, Nevada, Colorado, New Mexico and Virginia all flipped between 2004 and 2008, and have been the same for the last 3 elections. That brings us down to 8 states that are most likely for our hypothetical democrat to be able to flip, or for Trump to focus on holding.

Now, there are two key factors to examine if we wanted to predict all eight of those today: the starting point and the direction of travel. Our starting point is the percentage of voters who voted Trump minus the number who voted Clinton – and, of course, note that all 8 of these recent swing states went for Trump in 2016. With this basic calculation, we can rule out three of the 8 as too difficult to swing: Trump crushed Clinton in Indiana by 19%, so it’s very unlikely to be taken back (this isn’t too surprising: other than Obama’s first election, it’s been Republican every election since 1992); and two lesser but still strong results – Iowa by 9.4% and Ohio by 8.1%.

Our final five show much closer margins:

North Carolina – 3.6%

Florida – 1.2%

Wisconsin – 0.7%

Pennsylvania – 0.7%

Michigan – 0.3%

Since we know those starting points, we should also consider the direction of travel: how have recent 2-term presidents done in their first election vs their second? With few data points over time, it’s hard to gather meaningful trends on this, but it seems to be declining over the last few decades. Reagan got 8% higher share in his second run, Clinton was down to 6%. H W Bush still went up, but only by 2%, and Obama went down by 2%. Now, the entire point of this article is to focus on specific places, not a flat percentage shift over the whole country, but assuming there is an equal shift, just 1% down for Trump in 2020 could mean him losing Wisconsin, Pennsylvania and Michigan, as above, and with that, the electoral college would crown his opponent the winner.

Taking our 8 states that have flipped in the last three elections, we also need to consider their electoral vote count. Hilary Clinton got 232 votes in 2016 (538 total, 269 to draw, 270 to win). Therefore, assuming all else stays the same, 38 more votes are needed for a Democrat to win in 2020.

As above, Iowa is probably already out of contention, but its six electoral votes means it wasn’t too important anyway. If the 2020 Democrat takes Florida’s 29 votes, that puts them at 259, so Wisconsin would make it a draw, and any of the other 5 would put them over. It’s worth mentioning here that in 2016, Clinton only narrowly took New Hampshire (by 0.3%), and it did go Republican as recently as 2000 and is worth only 4 electoral votes. But as above, if Florida and and Wisconsin bring it to 269 each, it could be a tiny state like this that makes all the difference.

Now, there is one final thing to examine to have the full picture: at the start of this article, we assumed that we shouldn’t target states that haven’t previously flipped in the last seven elections. But as some states become less swing-y over time, some states that were once solid can suddenly become swing states. We looked at 1992 to 2016, and 2004 to 2016, but 2016 itself was a very unusual election. The three states we have just decided are the most swingable in 2020 (WI, PA, MI), were not considered likely swing states before 2016: all three voted Democrat in all six elections up to 2012.

So what happened? These were not states that were in close contention after Obama – he won them all both times by around 10% each time.

We’ll examine what happened in the next article: why did Trump win 2016?