How? If we split by political grouping all the major population centers go Blue everywhere else goes Red? Unless we have a very polite split (unlikely in this case) the Blue side is just signing up to starve to death.
Blue population centers have a lot of money, and though expensive, importing food from other countries is always an option.
But not in a timeline fast enough to prevent them from starving.
There are plenty of places to buy food from if you do t have a xenophobic anti-trade president running your country.
No there really isn't, especially not in the timeline needed to prevent a city from starving. Seriously New York, Chicago, LA are all 2 weeks of supply chain disruption from foot riots. It takes a nation to supply mega cities like those.
You may not know this, but you can buy food. You don't have to grow it yourself.