When it comes to issues of race, immigration, national security, and environmental protection, they disagree about how the government should handle things like never before.
Relative to polls in the 1990s, Republicans are now much more likely to say poor people have it easy, while Democrats are less likely to say so. Conservatives are also more likely to say that environmental regulations are costing the US too many jobs. Liberals now seem less convinced that peace can be achieved through military strength than they were decades ago.
The Pew Research Center reports that the country's political divisions now far exceed "divisions along basic demographic lines, such as age, education, gender and race." The share of Americans who sit in the middle of the political spectrum is lower, too.
But what in the brains of conservative and liberal voters actually drive their belief systems? Scientists have been researching the psychological differences between people with different stances, and there are a few key ways that people on opposite ends of the political spectrum see the world.
Here's what the data shows:
Psychological differences between liberals and conservatives
Psychological differences between liberals and conservatives
Being scared can make you more conservative.
Decades of research has shown that people get more conservative when they feel threatened and afraid.
Threats of terrorism make everyone less liberal — researchers found this was especially true in the months after 9/11. During that time, the US saw a conservative shift, and Americans displayed increased support for military spending and for President George W. Bush.
Americans aren't the only ones whose political leanings are influenced by fear. A 2003 review of research conducted in five different countries looked into 22 separate tests of the hypothesis that fear fuels conservative viewpoints and found it was universally true.
A conservative brain is more active in different areas than a liberal one.
Brain scans show that people who self-identify as conservative have larger and more active right amygdalas, an area of the brain that's associated with expressing and processing fear. This aligns with the idea that feeling afraid makes people lean more to the right.
One 2013 study showed conservative brains tend to have more activity in their right amygdalas when they're taking risks than liberals do.
On the other hand, feeling safe and endowed with strength might make you lean a little more liberal than you otherwise would.
Groundbreaking research that Yale psychologists published in 2017 revealed that helping people imagine they're completely safe from harm can make them (temporarily) hold more liberal views.
The authors of that study said their results suggest that socially conservative views are driven, at least in part, by people's need to feel safe and secure.
That finding didn't hold true for people with economically conservative views, though.
Liberals are less squeamish about looking at yucky stuff like vomit, feces, and blood.
A 2018 study of college students showed that those with more socially conservative views were quicker to physically look away from disgusting images — like pictures of blood, feces, or vomit — than their liberal peers.
The self-reported social conservatives also stared longer at photos of other people reacting in disgust to icky stuff.
This latest research backs up other studies that have pointed out that conservatives are more easily grossed out than liberals.
A gut reaction of disgust is, evolutionarily speaking, a good thing for human species survival, since it helps us keep some foreign and potentially dangerous secretions at bay. But in our modern world, some research suggests this kind of aversion toward "impure" pathogens may also impact how people see others who aren't like them, including social "out-groups" like immigrants or foreigners.
Conservatives tend to display more ordered thinking patterns, whereas liberals have more "aha" moments.
A 2016 study at Northwestern University found that when conservative and liberal college students were given word problems to solve, both groups managed to arrive at some correct answers through gradual, analytical analysis. But when feeling stuck on a problem, liberals were much more likely to draw upon a sudden burst of insight — an 'aha' moment, like a lightbulb turning on in the brain.
This didn't mean that the liberals were any smarter than the conservatives. Rather, it showed that their brains had a tendency to reorganize their thoughts in more flexible ways, while the conservatives tended to take a more step-by-step approach. The researchers suggested that this finding may indicate that liberals and conservatives prefer solving problems in different ways.
Lead study author Carola Salvi said the results were consistent with what scientists already knew about the brains of people with different political leanings: "conservatives have more structured and persistent cognitive styles," she said in a statement.
Liberals tend to follow the wandering gaze of others more often, while conservative eyes stay more focused on the original subject they're looking at.
In 2010, researchers at the University of Nebraska tested whether conservatives and liberals physically see the world in different ways. They found that when it comes to matching the gaze of other people, the two groups differ.
The scientists measured this by having individual study participants watch a certain point on a computer screen and wait for a ball to show up in the frame. Then they added a distracting human face onto the screen — before the ball appeared. The face's eyes would look around. The scientists watched their participants to see if they followed the wandering gaze rather than focusing on looking for the ball.
The researchers found that the liberal participants tended to follow the direction of the eyes on the screen. Conservatives, on the other hand, weren't as swayed by their pixelated peers, and kept waiting for the ball.
That finding surprised the study authors.
"We did not expect conservatives to be completely immune to these cues," lead author Michael Dodd said when the study was released.
Holding conservative views seems to make people more resistant to change and help them explain inequality.
A 2003 review of decades of research on conservative people suggested that their social views can help satisfy "psychological needs" to make sense of the world and manage uncertainty and fear.
"People embrace political conservatism (at least in part) because it serves to reduce fear, anxiety, and uncertainty; to avoid change, disruption, and ambiguity; and to explain, order, and justify inequality among groups and individuals," the researchers said.
Liberal and conservative tastes in music and art are different, too.
Studies from the 1980s showed that conservatives preferred more simple paintings, familiar music, and unambiguous texts and poems, while liberals enjoy more cubist and abstract art.
Although that research dates back to a drastically different political climate more than three decades ago, the findings held up in more recent studies from 1997, 2010 and 2015. In 2014, Time magazine conducted an online survey and found that conservative readers tended to say they'd rather visit Times Square than the Metropolitan Museum of Art.
The finding fits with other research that also indicates conservatives tend to avoid uncertainty and dislike ambiguity.
Liberals are more likely to describe themselves as compassionate and optimistic, while conservatives are more likely to say they're people of honor and religion.
A 1980 study of high school students found conservative students at that time were more likely to describe themselves as "responsible," "organized," "successful," and "ambitious," while liberal students might describe themselves as "loving," "tender," or "mellow."
Surveys suggest that today's adults aren't much different than those 80s kids. A Pew Research Center study from 2014 showed that liberals were more likely than social conservatives to describe themselves as compassionate, trusting, upbeat, and optimistic, while conservatives were more likely to say they were people of honor, duty, religion, and proud to be American.
The self-reports go along with other more recent research from 2012, which suggests that liberals' top moral concerns tend to be about compassion and fairness, while conservatives are more concerned with loyalty, tradition, respect for authority, and purity.
Conservatives believe they have more self-control.
One 2015 study found that conservative students were often better at focusing their attention on a cognitive task called the Stroop color and word test. The common psychological study tool asks participants to quickly name the correct color of a word that's written on a different color background.
In the study, conservative students seemed to correctly answered the color questions faster than their liberal peers. The researchers think that's because the conservatives were more likely to believe in the concept of self-control.
"What we're finding is that conservatives are more likely to believe they can control their own behavior," psychologist Joshua Clarkson from the University of Cincinnati said when his study was released.
But the conservatives didn't always out-perform the liberals. When they were told that their free will might undermine their own self-control, they performed worse than their liberal peers.
"One could imagine a host of situations where knowing you are responsible for your actions could lead to frustration, anxiety and other negative emotions that could impair self-control," Clarkson said.
Liberals and conservatives extend feelings of compassion to different people.
New research shows that conservatives tend to express compassion to smaller social circles than liberals.
For example, conservative voters were found to be more likely to agree with statements like: "I often have tender, concerned feelings for my family members who are less fortunate than me."
But their responses suggested such feelings did not extend to people from other countries.
Liberals, on the other hand, were more likely to feel that same level of compassion for people around the world, and even to non-human and imaginary subjects like animals and aliens.