The (American) "western interior" states (the drier, more rural, less populated ones between the west coast and the center of the country (North and South Dakota, Kansas, Nebraska, Oklahoma, Texas) tend to vote Republican in Presidential elections. At least two exceptions stand out from the 2016 campaign:Colorado and New Mexico. These two states voted Democratic in 1992, 2008 and 2012 as well (New Mexico in 1996 and 2000).

I've come up with what appears to be a plausible explanation: Prior to Roe v. Wade, abortion was less restricted (green on the first map) in New Mexico, Colorado, (and Kansas), than in most other states of the United States.

Have any political scientists (or historians) cited views on abortion as to why Colorado and New Mexico have more "Democratic" tendencies than their neighbors? Are other issues cited such as e.g. environmentalism?


In the United States, large cities tend to skew Democratic. Denver's combined statistical area, which currently makes up 3.62 million of Colorado's 5.75 million people, represents 63% of the state's population. As Denver and it's surrounding metropolitan area have grown, so has the "blueness" of the state of Colorado.

Denver County gave 73.7% of its votes to Hillary Clinton in 2016, neighboring Arapahoe County gave 52.8% of its votes to Clinton, neighboring Jefferson County gave a plurality of 48.9% of votes to Clinton, Boulder County gave 70.3% of votes to Clinton, etc..

In other words, the larger the metropolitan area's share of the state population, the larger the vote share will be for Democrats with little exception.

I'm defining large cities as population centers with more than 1 million people.


New Mexico has a large Hispanic population in percentage. Colorado has a relatively large Hispanic percentage so the explanation is urbanization.

The rest of the states aren't blue because they're rural. Utah is Mormon, and Arizona is expected to go blue in 2020.

Arizona, for now is redder than CO or especially NM because of its history.

It should be noted that Nevada has voted Democratic in the past 3 presidential elections and is expected to do the same again this week.

Texas is a bit tricky. Trump is ahead by 3 points in the Economist's model and the state looks like it is getting bluer.

  • Worth noting that there were no truly large population centers in Arizona or Nevada before air conditioning and major federal water projects made them capable of sustaining large populations. Those states are less red than their population densities would suggest in part due to a large influx of retirees due to favorable income tax policies and warm weather. – ohwilleke Nov 3 '20 at 23:30

I'm going to focus more on New Mexico here, because I think that the explanation for Colorado (save for a few southern counties that are culturally much more similar to northern New Mexico than the rest of Colorado) is urbanization, as stated in the other answers.

To summarize

The first thing to note is that if you flick through a couple of county-by-county presidential election maps, you'll see that the north-central counties of Taos, Rio Arriba, Santa Fe, Mora, and San Miguel often vote the same way. This region is responsible for a lot of the cultural identity of New Mexico, and have strongly influenced the structure of its government. The political views of these counties have also started to line up with more urban counties like Dona Ana, Bernalillo, and Sandoval as urban areas have become steadily more blue throughout the 21st century. This political alignment between the cultural and population centers of New Mexico has led to it becoming decidedly bluer than many of the surrounding states, where an area as rural as Northern NM would almost assuredly be overwhelmingly conservative and might offset the liberal lean of the urban areas.

A history of northern New Mexico

It's worth taking a closer look at the history of this, since it's interesting and rarely discussed outside of New Mexico. The thing that makes north-central New Mexico different from a lot of the other western interior states is a culture that is much older and distinct from the other states in that category, due to the history of how it was colonized. To greatly generalize, after the introduction of horses to North America but pre 1800s, much of the western US consisted of very sparse Spanish presence and indigenous populations that were either small and disorganized or very mobile and nomadic. This meant that by the time the treaty of Guadalupe Hidalgo rolled around in 1848 and westward expansion began in earnest, Anglo Americans quickly took political control of these areas and were able to leverage the newfound industrial capacity of the US to slowly but surely consolidate the once spread out native tribes into a small collection of reservations in areas less desirable for settlers.

This story was not the case in north central New Mexico when the Spanish first arrived in the late 1500s. The natives in this region lived in organized towns and practiced agriculture, similar to the arriving Spaniards and often more efficiently since they were used to the climate. This fact, combined with the isolation of the area, lack of natural resources to justify a heavy presence, lesser industrial capacity and technology to fuel a war, and a decisive coordinated revolt meant that the Spanish were never able to establish a successful mission system to convert natives like they had in California. Eventually, they more or less gave up on the goal of converting the natives to Christianity, and instead focused on settling the areas not claimed by the natives.

The focus on settlement rather than evangelism left New Mexico with a much stronger Spanish culture and population than other lands ceded in the Treaty of Guadalupe Hidalgo-- New Mexico's Spanish speaking population in 1848 was around 4 times the combined Spanish speaking population at the same time of what is now Arizona, Texas, California, and Colorado. Keep in mind that San Juan in Rio Arriba county was founded in 1598 and Taos pueblo around 1000-- by the time New Mexico became a territory of the US, even the Spanish settlements were as old as the US is today. Although the percentage of New Mexico's Hispanic population did drop drastically by statehood due to an influx of Anglo homesteaders, the strong culture and higher Hispanic population present meant that Spanish language and heritage was protected more than in other states, and that Hispanics received more political representation than they did in other western states during the 20th century.


The other answers make good points, but I'll elaborate a bit more about Colorado, where I live and have been involved actively in politics for the last 24 years.

Colorado was in living memory a much more conservative state, comparable, to Nebraska.

What changed?

  • The oil and gas industry, which used to be the dominant force in the Colorado economy became less dominant as Colorado's economy diversified, particularly into the tech industry. This was, in part, driven by substantial historical investments in higher education (many of which have not continued). The new, more diverse economy has grown rapidly. Oil and gas industries are strongly conservative. Other industries that have joined Colorado's economy, less so.

  • Colorado Supreme Court rulings from the late 1800s made it much harder to mine coal economically in Colorado where strip mining was basically banned, than in neighboring Wyoming, which prevented the coal industry from becoming important in the state. A strong coal industry is a conservative force in a state (see, e.g., Wyoming and West Virginia).

  • Many prominent Democratic political campaign contributors in Colorado come from a tech industry background, an industry that didn't previously exist in Colorado. Several of these prominent Democrats have made a coordinated, strategic effort to make the state more Democratic leaning, for example, by pushing reforms to make voting easier and to make redistricting more balanced.

  • Military bases have become less important in the state's economy as several have been closed or downsized (e.g. Lowry Air Force Base in Denver). Few soldiers per capita tends to make a jurisdiction more liberal.

  • Municipal purchases of water rights from farmers have reduced the importance of irrigated farming in the economy in parts of the state.

  • Places with higher population density are more liberal. The economic growth discussed above led to population growth. And, key geography factors have forced Colorado to build new housing with higher population density that you would naively expect in places with lots of flat territory that is undeveloped or farmland.

In the resort towns in the mountains, mostly along I-70, mountainous terrain means that population densities are much greater than they look on a map or comparing county land area to populations. High rise living and public transit use, for example, is common in Colorado's mountains. This happened because skiing became a commercially viable activity in Colorado in the late 20th century.

Near major cities like Colorado Springs, Denver, Fort Collins and Grand Junction, scarce supplies of water available for municipal uses have forced new subdivisions to be more compact than they would otherwise. To build a new house in water scarce exurban Denver, you have to pay about $100,000 for the privilege of being hooked up to municipal water services, before buying land, building anything or paying development impact charges.

  • There have been lots of college educated migrants to Colorado from the Pacific States and the Northeast to fill the needs of a more diverse economy. Those migrants have brought their politics with them. As college educated whites have trended to the left, so has Colorado.

  • Colorado has a large and growing Hispanic population. Some families date back hundreds of years (especially in Southern Colorado that used to be part of Mexico). Some of the migration is more recent. Children of non-citizens a few decades ago when immigration from Latin America was heavier, are now voting citizens, and often their parents are now naturalized citizens. The Hispanic population has also grown at a higher rate from births less deaths than the population as a whole, in Colorado.

  • More recently, Colorado's position at the forefront of states legalizing recreational marijuana has drawn in new migrants, some in the industry and some attracted by legal marijuana availability, further diversifying the state's economy with generally liberal leaning migrants.

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