It hardly took another study for people to know that political polarization in this country is deeply embedded. Still, a report issued Monday by the Pew Research Center paints a particularly stark portrait of a nation in which the most significant divisions are no longer based on race, class or sex but on political identity.

For 25 years, Pew has been conducting regular surveys assessing American values. They provide a series of historical benchmarks by which to examine the changes in what binds people and what divides them. The latest report finds considerable continuity over that quarter-century in the way different groups view society — and one very large change.

“Overall, there has been much more stability than change across the 48 political values measures that the Pew Research Center has tracked since 1987,” the report states. “But the average partisan gap has nearly doubled over this 25-year period — from 10 percent in 1987 to 18 percent in the new study.”

Republicans and Democrats have long seen the world through different lenses. On some issues, the gaps between them are relatively small (the importance of political engagement, for example). On others they are wider. What Pew found is that in almost every measure, those gaps have increased over the past 25 years, and in some cases now seem to represent almost unbridgeable divisions.

The Pew report found that the changes began to accelerate during George W. Bush’s presidency. Barack Obama’s presidency, the report says, has received “the most extreme partisan reaction to government in the past 25 years. Republicans are far more negative toward government than at any previous point, while Democrats feel far more positive.”

Democrats and Republicans more divided than ever on values. (The Washington Post/Pew Research Center)

Andrew Kohut, who directed the study, said two things are notable. One is that, “by and large, values haven’t changed. The other is that political identity has eclipsed these other factors” such as race and class as the biggest sources of division. “The only thing that’s changed is the extent to which Republicans and Democrats go to opposite sides of the room on most issues.”

Some of the most significant differences — and the areas where the divisions have increased the most — were on core issues of the 2012 campaign: the role and scope of government and the social safety net.

Twenty-five years ago, the gap between Republicans and Democrats on how they assessed the scope and performance of government was six percentage points. Today it is 33 points. On support for the social safety net, what once was a 21-point gap is now 41 points. On environmental issues, the gap has ballooned from five points to 39 points.

On some of these issues, the biggest changes in attitudes have been among Republicans. Twenty-five years ago, 62 percent of Republicans and 79 percent of Democrats said the government should take care of people who can’t take care of themselves. Today, 75 percent of Democrats agree with that statement, but the percentage of Republicans who agree has plummeted to 40 percent.

The shift on environmental issues among Republicans has been even greater. In 1987, 93 percent of Democrats and 86 percent of Republicans said there should be stricter laws and regulations to protect the environment. In the latest survey, Democratic support is unchanged, but among Republicans it has plunged to 47 percent.

But Republicans aren’t the only ones responsible for the partisan polarization. In other areas, changes in attitudes among Democrats have widened the gap between the parties.

Although majorities of Democrats and Republicans express strong faith in religion, Democrats are less likely to say that today than in 1987. What once was a three-point gap between Republicans and Democrats on doubting the existence of God is now 15 points. The report found that among liberals, the shift away from religious values has been particularly pronounced.

Democrats are more supportive of immigration rights than they once were, while Republican support has declined somewhat. The percentage of Democrats who say government should do more to ensure equal opportunity for blacks and other minorities has risen, more so than the decline among Republicans.

The most profound change may be on the issue that has roiled American politics since early in Obama’s administration: the role of government.

“Since 2007, Republicans increasingly feel that regulation does more harm than good, while Democrats increasingly disagree,” the report states. “Republicans see more waste and inefficiency, Democrats see less. And the share of Republicans who say the government is too involved in our daily lives has grown, while the number of Democrats who say this has decreased.”

Americans long have been divided along partisan as well as demographic lines. The report states that 25 years ago, the cleavages between Republicans and Democrats were “on a par with the differences of opinion between blacks and whites, wealthy and poor or college grads and those without a college degree. This is no longer the case. Since 1987 — and particularly over the past decade — the country has experienced a stark increase in partisan polarization.”

Part of this is related to the growing homogenization of the major political parties, a sorting out that has been going on for some time. More Republicans now call themselves conservatives (over the past 12 years, that percentage has risen from 60 to 68) and more Democrats now consider themselves liberal (increasing from 28 percent to 38 percent since 2000).

Over this period, the Democratic Party has become more diverse, with minorities now accounting for 45 percent of those who call themselves Democrats, up from 36 percent 12 years ago. During that same period, Republicans have remained overwhelmingly white in their makeup, at about 87 percent.

The changes the report cites have taken place at a time when the percentage of Americans who describe themselves as politically independent has risen sharply. Citing data from the Gallup organization, the Pew study states that it is probably safe to say that there are more independents than at any time in the past 75 years.

But the increasing partisan divisions cannot be attributed to the fact that the two parties are smaller and more ideological. Many who call themselves independents actually lean toward one party or the other. The Pew study states: “Even when the definition of the party bases is extended to include these leaning independents, the values gap has about doubled between 1987 and 2012.”

Americans may bemoan partisan gridlock in Washington, but they need only look at the report to understand the root of the problem. Polarization in Washington is not just politicians behaving badly. It reflects what is happening around the country. Partisanship has grown dramatically and shows no sign of abating in the near future.

For previous columns by Dan Balz, go to postpolitics.com.