The UK is smaller than 10 (11 if you count Illinois waterways) of the 50 US states.
You're talking about a country whose states range in all manner of ways and cultures. I always say it's worth thinking of Europe as one country to get an idea of the way things play out in the US.
The election only comes down to a handful of states though, they don't even need to campaign in say California, New York, Illinois, Connecticut etc.