
The State Similarity Index attempts to quantify how similar states are to each other relative to other states. The index is a statistically-based way to measure this. 20% of the index is based on politics. 16.66% of a state’s political score (3.33% of the overall State Similarity Index score) is allocated for the state’s executive branch preferences in the last five contested elections. The following is an explanation on how they were calculated:


Presidential Election
In the last five presidential elections, many states have always voted for the Republican candidate, while other states have always voted for the Democratic candidate. All the states on the West Coast vote for Democrats, except for Alaska. The same goes for most of the Northeastern states. The reverse is true for states in the South and many rural Western states with a low amount of racial diversity. In the recent decades, these states always vote for Republicans. The Great Lakes region is neither especially Democratic nor especially Republican heavy, since it is the most average region in the country. Iowa and Ohio have voted two times for Republican candidates and two times for Democratic candidates in the past four elections. Florida is another state that Obama was able to win twice, unlike Joe Biden and Hillary Clinton.
Source: 270 to Win
Categories: Democrat, Republican


Governor Election
In recent years, several states choose governors from one party while electing presidents from another. For example, Republicans won governorships in Vermont and Massachusetts in 2016, although they voted for Hillary Clinton for president. Montana and West Virginia are two states that have often had Democratic governors in the past decades, despite always voting for Republican presidential candidates in recent elections. In addition, Alaska and Rhode Island have had independent governors in recent years. These examples highlight the diversity of political preferences and dynamics in different states, with voters often making distinct choices for governor and president based on regional, ideological, or other factors.
Source: 270 to win
Categories: Democrat, Republican, Independent


Democratic Presidential Primary Election
Presidential primary candidates have less stark contrasts in political views than in the general election. Many Democratic presidential primaries have had clear winners. Two exceptions were Clinton vs. Obama and Clinton vs. Sanders. In the 2008 primary, Barack Obama tended to do better in states with more African Americans, but also states with high percentages of White progressives. Hillary Clinton did better in states with high populations of Latinos. In 2016, Bernie Sanders, did well in states with high percentages of White people, but failed to win many more diverse states. However, in 2020 Sanders did win the California and Nevada, two state with a high percentage of Latinos.
Source: The Green Papers
2020: Biden, Sanders, Buttigieg
2016: Clinton, Sanders
2008: Obama, Clinton
2004: Kerry, Edwards, Dean, Clark
2000: Gore


Republican Presidential Primary Election
In general, the less conservative Republicans do better in Northern states, while more conservative candidates do better in the Southern states. Unlike the Democratic party primaries, there is less obvious contrast in voting between rural states with little diversity and more urbanized states with more diversity. This is because the Republican party is mostly White even in the most diverse states. In fact, only White males have ever won state primaries. Marco Rubio and Ted Cruz could be considered Latinos, but they have White ancestry.
Source: The Green Papers
2016: Trump, Cruz, Rubio, Kasich, Uncommitted
2012: Romney, Santorum, Paul, Gingrich
2008: McCain, Romney, Huckabee
2000: Bush, McCain
1996: Dole, Buchanan, Forbes