The US is divided in terms of its two major parties, with Democratic controlled states known as blue states and Republican controlled states known as red states. Here is a map that shows the urbanization of America.

 

 

So, given that 80% of people live in urban areas, you can see above where those areas are. Now let’s look at the last 4 presidential elections.

 

 

In this map you can see that (with the exception of Georgia and Texas), states with major urban areas tend to vote democratic more often than not. I lived in Atlanta for 6 years and during Obama’s campaign there was a majority of popular opinion for him there but that stopped outside of the city limits. I’m assuming it is similar to major urban areas in Texas as well.