The US Senate is deliberately non-democratic. This is known. How it got this way goes beyond the Connecticut Compromise, however, and the advantage to the GOP doesn’t necessarily come from where you think it might.

It is well-known that the United States Senate disproportionately favors less populated states. Wyoming, our nation’s least populated state, has two senators for its population of roughly 580,000 people. California, meanwhile, also has two senators for its population of over thirty-eight million people. Meaning that the average citizen of Wyoming has Senate representation greater than sixty-six times that of the average Californian.

Disparities in upper houses aren’t unique to the United States. In Germany, each of the states have between four and six members of their upper house (the Bundesrat). Though it’s is apportioned by population, but that doesn’t come close to accounting for a population disparity where the least populace state has 600,000 and the most populous over seventeen million. Like the United States, Australia’s upper house gives uniform senate representation despite significant population disparities. Canada’s upper house representation is hard-coded into their constitution in such a way that New Brunswick (population 750,000) has ten senators while British Columbia (population 4,400,000) has only six.

The circumstances in all of these upper houses are different, of course. They also have different powers and responsibilities, with some having more than others and few having as many as the United States. In the Bundesrat, the members are appointed by the state executives, while in Canada they are appointed by the Prime Minister.

What makes the United States unique is the combination of how selection occurs, the scope of the population disparity, and the amount of power enjoyed by the senate. Not just by virtue of the fact that (unlike Australia, Canada, Germany, and others) we don’t have a chief executive derived from the other house, but because of custom, legislative rules, and powers specifically given to it in the Constitution. All of which make the sheer size of the population disparity more contentious.

This wasn’t accidental, of course. It was the compromise between the large states and the smallest states at our nation’s founding. James Madison and Edmund Randolph wanted representation in accordance with population for both houses, while William Patterson wanted representation to be divided equally by state. The result was the straightforward Connecticut Compromise, which gave took advantage of the bicameral legislature and fashioned one house by each preference. Until the 17th Amendment, the senators were appointed by state legislators and ostensibly represented the states themselves rather than the people therein – a distinction not everybody recognized – so in that sense it makes sense that each of them have an equal seat at the table. When senators became elected by, and representative of the people, however, this distinction was blurred. It can be easier to question why a voter in Wyoming has so much more senate representation in California when voters in Wyoming and California alike are voting to elect senators.

In addition to how senators were elected being different as they are now, it’s also worth noting that the population disparities at the time were not so great as they are now. By the time of the first Census in 1790, the least populous state, Rhode Island, was just shy of 1/10 the population of Virginia, the most populous state. That gap closes further when we consider that a disproportionate number of Virginia residents could not vote. By 1860, the gap had spread to Rhode Island being roughly 1/22 the size of New York, the most populous state at the time.

Statehood admission in the pre-Civil War era was largely geared towards maintaining a balance between free states and slave states. Consideration also included partisan affiliation and cultural integration. It rarely, however, considered population except in the most extreme terms. More extreme, I should add, than the California/Wyoming divide is now.

In fact, Wyoming was admitted into the union in 1890, in rough proximity to North Dakota (1889), South Dakota (1889), Montana (1889), Washington (1889), and Idaho (1890). Wyoming’s population in 1890 was around 62,000, making it barely more than 1/100 the population of New York, one quarter the population of DC, and less than half the population of any other state besides Idaho. It was smaller than Oklahoma, Arizona and New Mexico, which hadn’t been admitted due to concerns about their Amerindian and Hispanic populations. There was little expectation that Wyoming would experience a population boom as it lacked for natural resources and bringing people into the state had always been a struggle.

The primary reasons that the six states were admitted to the union were partisan. It was expected that the six new additions would be Republican states. In fact, they didn’t vote in anything resembling a block. Four of the six supported Republican Benjamin Harrison’s re-election with the other two going to People’s Party candidate James Weaver. Four of the six went on to support Democrat William Jennings Bryan over McKinley, then four for six for McKinley over Bryan. Had this been known, it’s entirely possible that they would have been admitted as states sooner than they were.

However, it is not actually Wyoming that is the outlier in the modern day as Vermont is not far behind. It’s California.

When California became a state, the nation had bigger concerns than allowing too large a state to join. California had wide latitude in deciding its own borders due to the leverage it had. It drew its own borders, which would later form a significant population. Just as Wyoming’s lack of population was foreseeable, so too was California’s robust one (though it was more reasonable, at the time, to believe that the population would be weighted more to the north). Had California wanted to be two states with four senators, they almost certainly could have. There was movement in that direction, though it died with the Civil War.

The story in California is actually not unique. From Texas to Deseret, many states had the ambition of being larger than the national government wanted them to be. There are counter-examples, too, such as Arizona’s objection to being admitted as a single state with New Mexico. There are also various cases of farmers not wanting to deal with miners and wanting the state borders drawn accordingly. Concerns about states being too large, however, have historically been on the federal side of the negotiation table.

It is conventional wisdom that the Senate favors Republicans, by virtue of the fact that the Republican Party has its strongest inroads in rural and sparsely populated place. Further, when we think of low population states, we often think about those giant blocks in the west that are so often reliably Republican states.

The conventional wisdom that the Senate’s disproportionate representation favors Republicans is correct. Not for reason that most often comes to mind. The small states have little to do with it. In fact, the least populated states give a partisan advantage to the Democrats.

Why?

The first is that how we approach small population states is misleading. We often think of Wyoming, Montana, and the Dakotas because they are so visible when we look at a map. Also in the small population group through are Rhode Island, Vermont, and Delaware, all of which are easier to miss. Further, the Democrats are surprisingly competitive in lower-population Red States, while the same is only true to a lesser extent (Maine and New Hampshire, mostly) of the Blue States.

Regardless, as the Senate currently stands, among states with under one million people, there are seven Democratic senators and five Republicans. For states with under two million people, the Democratic advantage expands to a 19-11 advantage. It is only once we pass two million people that the Republicans start doing extremely well. From there, the larger a state gets, the more likely it is to vote Democratic in senate elections. With some obvious exceptions, of course, like Texas. Among states with over six million people, Democrats hold a 20-14 advantage.

So it’s the middle-sized and larger states where the Republican advantage truly lies. The advantage is not insignificant, though at the moment it is actually less than one might think. The Democrats hold a 55-45 lead in the Senate, which if dispersed by population would actually look more like 58/42 split. On the one hand, we would not be talking about a potential Republican take-over the Senate if this were so. On the other hand, the Democrats would still be shy of a Filibuster-proof majority.

This is all subject to change from election to election, and the 2014 election in particular represents just the sort of thing that Senate critics are complaining about. The Republicans are poised to reach parity in the Senate based largely on the advantage of small states with fewer than two million people: Montana, South Dakota, and Alaska. If the Republicans win in those three states, plus Arkansas and Louisiana, they will have 50 Senate seats despite barely increasing the number of people they actually represent. The three-seat disparity between a people-representative senate and the current state-representative senate would open up to seven.

Even then, the strength of the Republican advantage lying mostly in the middle-third of states instead of the bottom-third.