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

Your question touches decades of shifting politics — I'll pull the historical trends and recent data to see how today's divide compares.

Political polarization is more pronounced now than in the recent past, but whether it is worse than any time in the past depends on the time frame and measure used:

1. Compared to the last 25-50 years: Yes, at historic highs

> As Americans head to the polls this November, their values and basic beliefs are more polarized along partisan lines than at any point in the past 25 years

> Unlike in 1987, when the Pew Research Center began its series of surveys on American values, the gap between Republicans and Democrats is now greater than gender, age, race or class divides

> During this time, the average partisan gap has nearly doubled — from 10 percentage points in 1987 to 18 percentage points in the new study

Across 48 different questions "the average difference between the opinions of Republicans and Democrats now stands at 18 percentage points…nearly twice the size of the gap in surveys conducted from 1987-2002"

> Indeed, a Pew Research Center analysis finds that, on average, Democrats and Republicans are farther apart ideologically today than at any time in the past 50 years

Between the 92nd Congress of 1971-72 and the current 117th Congress, for example, House Democrats moved from about -0.31 to -0.38, while House Republicans moved from 0.25 to nearly 0.51

> 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

Using the standard political science measure DW-NOMINATE, based on members' voting records:

> the standard DW-Nominate measure reveals a higher level of polarization in both chambers than at any time in the history of the two major parties

> The results from DW-NOMINATE indicate that the level of polarization in Congress is now the highest since the end of the Civil War and shows no sign that it will abate

Polarization had risen in the Senate since the mid-1950s and in the House since the mid-1970s

2. Affective polarization - dislike of the other side - also sharply increased

Researchers distinguish ideological polarization (disagreement on issues) from affective polarization (feelings toward the other party).

> in the US, affective polarization has increased more dramatically since the late 1970s than in the eight other countries they examined—the UK, Canada, Australia, New ...

In that multinational study, the U.S. pattern was exceptional:

> 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

One summary noted:

> Levels of affective polarisation have risen more than two-fold since the 1970s when the American National Election Studies, a ... The gap had widened to 56 by 2020

Although other work notes:

> Although ideological polarization seems to be largely concentrated among political elites , affective polarization, or a general disdain for the other party, is pervasive among ordinary voters

3. Compared to the entire span of U.S. history: No, not the worst

Scholars stress historical context:

> That is to say, the extent of today's polarization looks one way if the point of comparison is 1859, on the brink of America's Civil War, or the 1950s, a decade frequently characterized as "the end of ideology"

Brookings analyses note:

> 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

And more fully:

> Today's social conflicts and partisan strife pale in comparison with much of the nation's past. Recall the racial apartheid that scarred America for a century after the end of slavery, and the urban riots and anti-war protests that inflamed the country during the 1960s

Historian Gary W. Gallagher argued:

> As a historian who has written and taught about the Civil War era for several decades, I know that current divisions pale in comparison to those of the mid-19th century

Between Lincoln's election and Lee's surrender the nation literally broke apart, with

> Four years of civil war produced at least 620,000 military deaths

Other periods cited as more polarized include the 19th century battle between slaveocrats and abolitionists; the 1890s struggle between agrarian populists and an emerging business/manufacturing class; and the divide in the 1930s

In short: By measures of ideology in Congress, partisan sorting, and mutual dislike since the 1970s-1980s, polarization is worse than at any point in the last 50-150 years of the two-party system. By measures of violence, secession, and existential national rupture, it remains less severe than the Civil War, Reconstruction, and other earlier eras.