I could hop in my car and drive all the way from the west coast to the east coast and never pass through a blue county. Likewise, I could start at our southern border and drive all the way to Canada without ever passing through a blue county.
You know why? Because mainstream America extends from coast to coast. The Democrats power is derived from large population centers where a high percentage of constituents are dependent on the state (welfare, etc).
One need only look at the map to see this is true.