We hear a lot these days about red states and blue states, but what does that really mean? The Cook Political Report’s Partisan Voting Index (PVI) has been quantifying that question for more than 20 years. 

The Cook Political Report is an online source for non-partisan political analysis that many rely on for accurate political forecasting. The PVI assigns a numeric score to each U.S. congressional district based on how it performed in the previous election compared to the country as a whole. 

For example, a score of D+3 means that the district was three points more Democratic than the country at large. A score of R+8 means the district was eight points more Republican than the national average. Districts that are in line with the national average receive a score of “EVEN.” These average districts include Florida’s 7th district, California’s 10th district, and Oregon’s 4th district.

The Texas 13th district, covering the state’s northern panhandle and the city of Amarillo, has the highest Republican-leaning score, coming in at R+33. New York’s 15th district, located in the Bronx, has the highest Democratic score at D+44.

 As we head into next year’s election, let’s take a look at what we are likely to see based on how partisan the states really are.

Reliably Red

Large portions of the U.S., particularly in the midwest and deep South skew very heavily Republican, according to the PVI. Several states in this region, including North Dakota, South Dakota, and Wyoming, only have one congressional district — effectively making the PVI ranking statewide.

Wyoming is rated R+25, with nearly 70 percent of voters supporting Donald Trump in 2016 and Mitt Romney in 2012. Nebraska has two congressional districts at R+4 and R+27. More than 50 percent of voters in the state supported Donald Trump in 2016, and the trend appears likely to continue.

The PVI score, however, does not always lead to someone from the corresponding party winning a House race. Oklahoma has five congressional districts ranging from R+10 to R+27. In 2018 Kendra Horn became the first Democrat to win an election in the state’s 5th district, which scores R+10, in 40 years. 

Tried and True Blue

The heavily Democratic parts of the country tend to be clustered in New England and along the West Coast. The only Republican-leaning districts in New England are in rural regions of Maine and New Hampshire, and even those are only scored R+2.

More than two-thirds of California’s 53 congressional districts lean Democratic, as do those in the southern half of Texas and the eastern coasts of Oregon and Washington. 

Democratic support also comes from the areas around major cities. Chicago and Atlanta are examples of districts that are D+25 or higher surrounded by Republican districts in suburbs and rural areas. As younger people continue to move to cities for jobs in technology and other sectors, this trend appears likely to continue

Somewhere in the Middle

Of course, nothing is completely cut and dry. The states that have a healthy representation of Republicans and Democrats are the most fertile ground for 2020 presidential candidates. These states include Pennsylvania, Wisconsin, Ohio, and Michigan. 

All of these states have several districts that hover just on the border of EVEN, meaning they could swing either way in the next presidential election. Expect to see President Trump and his Democratic opponents spending lots of time in these states between now and November 2020. 

Pennsylvania and Wisconsin are also in the process of drawing new congressional districts after accusations of partisan gerrymandering. The composition of those new districts will likely change the PVI rating and could impact how those states are represented in Congress moving forward. 

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