At the center of the broken senate is something all American schoolchildren learn: Every state gets two senators.

This chart shows every US senator in 1950 and how many people they represented.

Since every state gets two senators, regardless of population, some senators represent a lot of people – and others represent very few. This has always been true.

This disproportionate representation wasn't a huge deal in 1950. About an even number of Democrats and Republicans represented big states and small states.

We can see this a lot more clearly when we organize the 1950 senators by party.

In 1960, Democrats held a lot more seats but that's because they won a lot more votes across both small states and big states.

That mostly held true through 1970.

But by 1980, a trend started to emerge: Democrats were far more likely to represent bigger states, while Republicans represented many small states.

And this trend got more pronounced in 1990.

Because of this trend, the senate started to structurally favor Republicans.

In 2000, Democratic senators represented nearly 3m more people than Republican senators – but Republicans still held the majority.

In 2010, Democratic senators represented 74m more people than Republicans – but they still failed to hold a supermajority.

In the decade since, the structural Democratic disadvantage has only gotten worse.

Currently Democratic senators represent 42m more people than Republican senators – but the senate is split 50-50.