Cook Partisan Voting Index (PVI)

Another metric measuring party preference is the Cook Partisan Voting Index (PVI). Cook PVIs are calculated by comparing a state's average Democratic Party or Republican Party share of the two-party presidential vote in the past two presidential elections to the nation's average share of the same. PVIs for the states over time can be used to show the trends of U.S. states towards, or away from, one party or the other.^[4]

Gallup

On December 17, 2020, Gallup polling found that 31% of Americans identified as Democrats, 25% identified as Republicans, and 41% as Independent.^[5] Additionally, polling showed that 50% are either "Democrats or Democratic leaners" and 39% are either "Republicans or Republican leaners" when Independents were asked, "do you lean more to the Democratic Party or the Republican Party?"^[5]

In 2018, the number of competitive states according to opinion polling dropped down to 10, the lowest number since 2008. From 2017 to 2018, New Hampshire, Nevada, and Pennsylvania moved from competitive to lean Democratic, while West Virginia, Louisiana, and Indiana moved from competitive to lean Republican, and Nebraska moved from lean Republican to competitive.^[6]

As of 2018, Massachusetts was the most Democratic state, with 56% of residents identifying as Democrats, while only 27% of residents identified as Republicans. However, it is important to note that Washington D.C. (while not a state) has 3 electoral votes and 76% of residents identify as Democrats, while 6% identify as Republicans. Wyoming was the most Republican state, with 59% of residents identifying as Republican, and only 25% of residents identifying as Democrat.^[6]

Voter registration

The state Democratic or Republican Party controls the governorship, the state legislative houses, and U.S. Senate representation. Nebraska's legislature is unicameral (i.e., it has only one legislative house) and is officially non-partisan, though party affiliation still has an unofficial influence on the legislative process.

The simplest measure of party strength in a state voting population is the affiliation totals from voter registration from the websites of the Secretaries of State or state Boards of Elections for the 31 states and the District of Columbia that allow registered voters to indicate a party preference when registering to vote. 19 states^{[lower-alpha 1]} do not include party preference with voter registration. The party affiliations in the party control table are obtained from state party registration figures where indicated.^[7]

As of October 2022, a plurality of voters in California, Nevada, New Mexico, Louisiana, Delaware, New Jersey, New York, Pennsylvania, and Maine are Democratic, while a majority of Maryland voters are Democrats. Meanwhile, a plurality of voters in Arizona, South Dakota, Nebraska, Kansas, Iowa, Kentucky, West Virginia, and Florida are Republicans. A majority of voters in Utah, Idaho, Wyoming, and Oklahoma are Republicans. In Oregon, Colorado, North Carolina, Connecticut, Rhode Island, Massachusetts, and New Hampshire, a plurality of voters are Independents. While in Alaska and Arkansas, a majority of voters are independents.^[8]

U.S. state party control as of April 2024

State government