There is no guarantee that this bias will persist. If Republicans keep gaining in rural areas and Democrats keep gaining in the suburbs, Republicans might find themselves at an underlying disadvantage in the House.

And Democrats have one advantage of their own, in translating their votes to seats in the House: their ability to win districts with relatively few voters, often in heavily Latino areas with low citizenship rates, high numbers of children and low turnout. This advantage seems likelier to endure after the Supreme Court ruled against the Trump administration on adding a citizenship question to the census, which might have allowed states to draw districts based on the number of eligible voters, not the total population. (The administration has not given up in this effort, with President Trump saying the census may be delayed.)

But for now the overall bias benefits Republicans, and partisan gerrymandering often increases this effect. In blue-leaning states, it is easy enough for Republican governments to draw heavily Democratic districts, anchored in cities, then divvy up the rest of a state to their advantage, as they did in Pennsylvania or Michigan. In red-leaning states, they can break up cities into multiple Republican-leaning districts, as they have in Utah or Ohio. Over all, gerrymandering probably gives the Republicans about 10 more seats than they would have otherwise.

In an era of growing geographic polarization, these gerrymanders can be quite durable and can even become more effective over time. In 2018, Republican state legislative maps easily survived a Democratic wave election in states like Michigan and Wisconsin.

Other sources of disadvantage for large states

At the same time, the American electoral system disadvantages the party of populous states through the Senate and, to a lesser degree, the Electoral College. Every state gets two senators, regardless of population.

That has wound up disadvantaging Democrats as American electoral politics have polarized along geographic lines, since they tend to excel in the relatively populous states with big cities.

The Republican Senate advantage is similar to the Republican edge in the U.S. House, even though there’s no gerrymandering involved. The Democrats failed to take the Senate in 2018 despite favorable political conditions in part for this reason.