So what is it about D.C. statehood that gives Americans pause? The most obvious explanation might be that adding a state would change the electoral math. Washington, D.C., is a heavily Democratic city — for example, just 4 percent of its residents voted for President Trump in 2016 — so D.C. statehood would almost certainly give Democrats two more senators, one more seat in the House, and three more electoral votes, all of which could make Republicans less likely to support it.

But perhaps there’s something else going on here, as Americans haven’t always been opposed to adding new states. For instance, before Alaska became a state in 1959, 71 percent of Americans were in favor of adding it to the Union, according to a Gallup poll from 1957.2 And support for Puerto Rico’s statehood remains higher than support for the District’s. In Gallup’s most recent poll, they found that two-thirds of Americans favor statehood for Puerto Rico.

So it could be that Americans just don’t think of the nation’s capital as a state.