The argument, powered by the American Nations model, is historical, ethnographic, and cultural. Iowa is the only state entirely dominated by the Midlands, the key "swing" region of American politics, and exhibits its proclivities and priorities in their most unadulterated form:
[The big reason] Iowa deserves to keep its spot as a American political capital: Despite being home to just 3 million people, about 2.9 million of whom are white, Iowa is the state most reflective of the nation’s most vital swing region—a culturally diverse, politically moderate swath of the country that transcends state boundaries and has proved decisive in American politics for the better part of two centuries.
Ever since the first Euro-American settlers poured into Iowa in the decades leading up to the Civil War, the state has been an ethnological mosaic, a place where cultural diversity was not only expected and tolerated, but where no one group was expected to dominate. In this way—neither an Anglo-Protestant-led “melting pot” (as in the New England-influenced northernmost tier of the country) nor hierarchical, post-plantation society like the lowland south—Iowa exemplifies a vital, often ignored, and politically consequential American regional culture that I call “the Midlands,” which is central to American presidential politics.