This isn't really a criticism of the US Census Bureau, but I think the way they define
urban vs rural is insufficient. They're doing it to objectively quantify the data, which is literally their job, so their definition works for that purpose. However I think there's a
qualitative difference with the way people in sparse suburbs feel, even though they are included in a larger "urban" area.
The basic problem is urban sprawl turning into suburban sprawl. When you have an urban core and a traditional suburb outside it, the "escape the city" mindset is pretty clear. However, over the last 50 years, suburbs themselves have sprawled out, pushing into previously rural areas and turning them into semi-rural or less-dense suburb areas. This is partly because that's where the cheap land is, and partly due to the problems with a reverse move back into the cities.
You can see this in the "suburbs" of many cities: small houses on large 5 acre wooded lots, horse ranches and goat farms inexplicably next to brand new cookie-cutter McMansions, etc. The rural tracts got surrounded by developers, especially over the last 20 years, and just keep going while the chain stores and gated apartment complexes pop up in their areas.
So what is the mindset of that kind of resident? Someone who doesn't want the full rural experience, or the (relatively) closer community of the suburbs? Someone looking for more isolation, a quieter area? My theory is that they represent disenchantment with suburban homogeneity and lack of character, as the suburbs got built out in mass volumes. Maybe the desire to own some land, a proper homestead, instead of just a house and a lawn.
How do you characterize them, politically? Hard to say, since "semi-rural" isn't an accepted definition and it isn't fully studied yet. My theory is they represent a more conservative and isolationist swath of the suburban residents. If it were the opposite, they would want to move in the other direction, closer to the cities, and gentrify something.
If I'm correct, then the Census undercounts the number of people who
think they are living in a quasi-rural lifestyle, because the geography includes them in some larger urban center.