The people who designed the US government had a deep distrust of mankind and did not trust them to vote directly for the president. They therefore designed an indirect system that would in theory allow better-informed people to exercise their judgment. Unfortunately we saw in 2016 how dismally this system failed to prevent the very outcome that it was designed to prevent.
While voters presume they are voting for a candidate, in fact they are voting for electors who are pledged to vote for that candidate. Each state gets the number of electors equal to its representation in Congress, that is, the number of Representatives and Senators combined. There are 538 electors so it takes 270 to win. The electors meet in January in the Electoral College and formally elect the president. Normally this meeting is just a quaint formality, but as we shall see, this year may be different.
This system gives an advantage to the small rural states, because they have the same number of Senators as the larger states and at least one Representative. For example, Wyoming with 579k people gets three electors, while California with 39.5mn people gets 55. That means Wyoming has one elector for every 193k people while California has one for every 718k! There are seven states with fewer than 1mn population.
Even more important is the “winner-take-all” method of allocating electors. Almost all (48 out of 50) states give all their electors to whoever gets the most votes, even if it’s not a majority. Under this system, it is theoretically possible to win the presidency by winning a majority – or even a plurality, if there’s a third-party candidate – in just the 11 most populous states without getting even a single vote at all in the remaining 39 states. In 2016 Trump won six states without having a majority, thanks to the presence of third-party candidates. His margin of victory in Michigan was a minuscule 10,704 votes or 0.2% of the votes, but under the winner-take-all system it didn’t matter – he got all 16 of Michigan’s electors.
The Republicans have a built-in advantage, because they have more support in rural states. It’s how Bush II and Trump won the Presidency even though they lost the popular vote. Clinton had 2.9mn more votes nationally than Trump did but lost because of fewer than 80,000 votes in three states.
This is why Biden’s lead in the national polls doesn’t guarantee anything: it all comes down to the states. Political analysts estimate that he will need a lead of more than 3% nationally to win the Electoral College
Most states are reliably Democratic or Republican and therefore not actively contested. For example, California usually votes Democrat, so it would be a waste for either candidate to spend a lot of money there – because of the winner-take-all system, increasing the Democratic vote from 50.1% to 99% does nothing for the Democratic candidate, while raising it from 1% to 49.9% does nothing for the Republican (assuming no third—party candidates, of course).
Usually there are at most some 12 states that might vote for either party. These states, called “swing states” or “battleground states,” are the main focus of campaigning among the candidates. This year there are three in particular: Georgia (16 electoral votes), North Carolina (16), and Arizona (11). Florida (29), Pennsylvania (20), and Wisconsin (10) were considered “swing states” until recently but have shifted to “lean Democratic.”
The Electoral College is written into the US constitution and so would be difficult to change, but this “winner-take-all” system is not. It’s just custom. There is a movement to change it. The National Popular Vote bill would require states to give their electors to whoever wins the national vote regardless of who wins the state. Fifteen states with 196 electoral votes have already agreed. The program will go into effect when enough states to give a majority in the Electoral College agree to participate.