Most cities require complex supply chains to stay fed. People require medical supplies. The electrical grid would collapse. The military has run war games on this, 50% of the U.S. pop would be dead in a matter of months from starvation or illness
That’s a terrible idea. Even the deepest blue states have huge numbers of republicans/conservatives and even the deepest red states have huge numbers of democrats/liberals/progressives. It would do far more harm that good to split the country.