We are at a point in time when it is worthwhile to take a step back and look at the current state of affairs through the lens of recent history. The defeat of Mitt Romney by Barack Obama ten years ago prompted the Republican establishment to reconsider its appeal. Now, Romney frequently joins Democrats in opposing the right-wing president who succeeded Obama, including the president’s attempt to retain power despite losing his reelection bid.

What appeared to be a fairly standard partisan tension in 2012 has now become the subject of regular articles speculating about civil war or, at the very least, an increase in political violence. Americans from both political parties increasingly dislike the other. A former defense secretary who served under Donald Trump recently stated that the greatest threat to the country is “extreme partisanship.”

The American National Election Studies (ANES), run by Stanford University and the University of Michigan, polls Americans on their political views at the time of each presidential election. For decades, researchers have asked the same or similar questions during each cycle of the study. The end result is a collection of data that provides unique insight into how Americans’ political views have evolved over the last few decades.

ANES published a page last week that compiled how key trends have evolved. These statistics highlight the growing political divide.

Take a look at how people identify their own ideologies. Since the 1960s, Republicans have been far more likely than others to identify as conservative. Democrats were roughly equally likely to describe themselves as liberal or moderate. That began to change around 1994, when Democratic self-identification as liberal began to rise.

It has risen dramatically since 2004, despite a drop in “conservative” identification. Meanwhile, Republican identification as “conservative” has increased.

I’ve divided the party into racial groups because of the interesting divide between White Democrats and Black or Hispanic members. As I’ve previously stated, the recent surge in Democratic self-identification as liberal is largely due to Whites in the party.

What this tells us is that Democrats (primarily White Democrats) now see themselves as more to the left than to the center. In other words, closer to the ideological pole.

We can see this by looking at how members of each party perceive those ideological groups. The ANES includes a “feeling thermometer,” which asks respondents to rate how warmly they view a group or subject. A perfect score of 100 is a wonderful feeling.

Partisans’ attitudes toward opposing ideologies have deteriorated in recent years. Democrats were only 4 degrees more favorable to “liberal” than “conservative” in 1994. In 2020, the gap was 28 points, thanks largely to White Democrats. The Republican gap narrowed slightly, but only because it had been so wide for decades. However, there has been a decline in Republicans’ perceptions of “liberal” since 2004.

Of course, partisanship in Congress has shifted during this time. Voteview’s academic team evaluated voting patterns and discovered that the average ideology of caucuses in both chambers of Congress has shifted to the poles since 1963. As you may have heard, the movement has been much stronger among Republican members of Congress.

Another significant change has occurred since 2004. A popular trope a few decades ago was that the Democratic and Republican parties were functionally indistinguishable, with only minor differences on key issues. That sense (which was always stronger among independents) has waned. Most partisans and three-quarters of independents now believe there is a significant difference between the parties.

This is in addition to other amplifications, such as the fact that partisans increasingly identify as strongly partisan.

Now we add it all together. Americans, particularly members of partisan groups, are more likely to embrace the ideological poles, less likely to have positive views of the pole opposite their own, increasingly see the choice between Democrat and Republican as important and are more likely to identify themselves as strongly partisan in their views.

The result? A nation in which the political poles have grown more crowded and more hostile to those on the other side.