Is political polarization worse than it's been in the past?

Polarization is debatable — I'll pull current studies and historical measures to compare past and present intensity.

Short answer: By most modern measures, yes - but with important historical context.

1. By measures covering the last 50-100 years, yes - it is at a modern high

The dynamics behind that gap have been building for decades:

> Both parties have grown more ideologically cohesive. There are now only about two dozen moderate Democrats and Republicans left on Capitol Hill, versus more than 160 in 1971-72

> Both parties have moved further away from the ideological center since the early 1970s. Democrats on average have become somewhat more liberal, while Republicans on average have become much more conservative

The ideological overlap that once allowed bipartisan coalitions has disappeared:

> Five decades ago, 144 House Republicans were less conservative than the most conservative Democrat, and 52 House Democrats were less liberal than the most liberal Republican
> Since 2002, when Republican Rep. Constance Morella of Maryland was defeated for reelection and GOP Rep. Benjamin Gilman of New York retired, there’s been no overlap at all between the least liberal Democrats and the least conservative Republicans in the House

Other analyses using the same voting data frame it in longer terms:

> ideological distance between the parties began to grow during the 1970s to the extent that Congress is now more polarized than at any time since the late 1870s Reconstruction Era

> Political polarization between the two parties has grown to a point that Americans have not seen since the 1890s, and perhaps not since the 1850s when the nation was in the process of coming apart over the slavery issue

In that mid-century period:

> From the late 1930s into the 1960s, roughly half the members of the House and Senate were "moderates" as measured by their voting records. The parties had not yet separated into rival ideological camps

> In the early 1980s, the proportion of moderates in Congress dropped below 40 percent for the first time in the post-war era, and by the late 1990s it had fallen below 20 percent. Today fewer than 10 percent of the members of Congress can be called moderates

2. Affective polarization - how much partisans dislike each other - has risen fastest in the U.S.

Political scientists distinguish ideological polarization (distance on policy) from affective polarization (animus/distrust toward the out-party). The second has grown especially fast:

> According to our baseline estimates, the US experienced the most rapid growth in affective polarization over this period among the twelve OECD countries we consider

> They found that in the U.S., affective polarization has increased more dramatically since the late 1970s than in the eight other countries they examined—the U.K., Canada, Australia, New Zealand, Germany, Switzerland, Norway and Sweden

> Since the mid-1990s, affective polarization intensified more sharply in the U.S. than in most other Western countries

Pew and other surveys reflect that: Democrats and Republicans increasingly see each other as more closed-minded, dishonest, immoral and unintelligent, and worry about marrying across party lines more than across religious lines.

The sorting process behind this is also documented: liberal voters increasingly vote consistently Democratic and conservatives Republican, and that sorting is associated with increased affective polarization.

3. "Worst ever" is not accurate historically

When the window is expanded to 150-200 years, today's polarization does not exceed the most violent periods:

> Some political scientists have pointed out that — viewed within the context of data from the last two centuries — today’s levels of polarization are not such an alarming anomaly compared to those occurring during the time of slavery and similar points along the historical continuum

Brookings notes:

> for all the hype about the ruptures and partisan rancor in contemporary American society, the strife pales in comparison with much of the nation's past. There have been long stretches of American history in which conflicts were far worse

Examples often cited: a fundamental dispute over slavery plunged the nation into civil war, including violence in the Senate in 1856, and the highly polarized 1890s and 1850s.

One recent comparative review noted that while Political groups have moved further apart in recent years, but these divisions are still fuzzy, and Americans are not split into entirely opposing tribes when it comes to the issues.

In other words:

Much of the difference today is also about consolidation and sorting - people now get clear cues from elites about what goes together, so someone with left-wing views on one issue is less likely to hold right-wing views on another than in the past - which makes divisions feel more total.