The food production level, however, is exponentially higher -- not a trivial factor.

Then again the number of people that buy the food is quite high. Farmers need non-farmer people to buy food as much as non-farming people need farmers to grow it.

While this assumption is correct assuming a functional republic, what if the republic isn't functional? Those low population density areas can easily sustain themselves with considerably less production output needed and less cost to produce. However the high population density blue areas would have a tough time adapting if those big red swaths of corn dried up for them. Ditto for red state energy sources too.

The problem with the blue states (and it’s actually just giant blue cities that make these states blue) in a hypothetical republic breakup scenario is they don’t necessarily provide a viable industry or commodity whose wealth can sustain their demand. Short of wood/lumber, there is not a lot of valuable commodities there that could be exported to buy the food and energy needed to maintain the blue cities, which would quickly shrink.

>The problem with the blue states

I had to look up what a "blue state" is. That's not a common concept outside the US. Most countries have a politically diverse make-up multiples parties over a range.

By corporate farms with lots of federal subsidies.

The fertilizer comes in from further away, hard to keep that high production level up without chemical fertilizer.

Yes, from other red states.