Partisan differences now divide Americans more sharply than distinctions of race, religion, education or sex as a decade-long wave has pushed Democrats and Republicans to opposite corners on a wide range of formerly less partisan issues.

On matters as disparate as environmental protection, support for the social safety net and immigration, former areas of bipartisan agreement have dissolved as Democrats have moved left and Republicans have shifted to the right, according to a major new study by the Pew Research Center, which has tracked American values over the last 25 years.

That polarization has important practical consequences -- forecasting continued gridlock in national politics.

One of the hottest debates among people who study American politics centers on whether the trench warfare so obvious in Congress mostly involves conflicts among elected officials and political interest groups or reflects a deeper divide among voters. Are politicians ignoring constituents’ desires for bipartisan solutions or representing a divided electorate all too well?

President Obama first became nationally famous in 2004 in part for a memorable statement of one side of that argument: “There is not a liberal America and a conservative America,” he said in a speech to the Democratic convention that year, “there is the United States of America.”

That sunny picture of national consensus has fared poorly during Obama’s presidency. Now the Pew study joins a growing body of data and analysis which rebuts the belief that voters are far more unified than their elected representatives. The study was based on a survey in April of more than 3,000 adult Americans and has a margin of error of +/-2.1 percentage points.

Americans “are more polarized along partisan lines than at any point in the past 25 years,” the study’s authors say. The average gap in views between Democratic and Republican partisans has nearly doubled, with most of the increase coming during the Obama and George W. Bush presidencies, Pew’s research found. Moreover, people’s consistency in hewing to one side or the other has increased.

“There are more people who are uniformly on the right or left,” said Michael Dimock, Pew’s associate director for research.

Pew researchers developed an index of several questions to test ideological consistency -- to see, for example, if a person who supports the social safety net also takes a liberal stance on affirmative action. Using that measure, they found that the percentage of both consistent liberals and consistent conservatives has risen. In 1987, fewer than one-in-three Americans fit into one of those two ideological categories; today 44% do.

Americans, particularly Democrats and independents, do say they want compromise. Asked if they agreed with the statement, “I like political leaders who are willing to make compromises in order to get the job done,” 80% in the survey said yes. Support for compromise has grown among Democrats over time, from 77% in 1987 to 90% now. Among Republicans, the number has remained fairly constant and now stands at 68%.

But on substantive issues, particularly those on the scope of government, which is at the heart of the battle that has divided Congress for the last year and a half, the gap in views leaves little common ground.

About three-quarters of Democrats, for example, say that the government has a “responsibility to take care of people who can’t take care of themselves.” Among Republicans 54% reject that idea, and only 40% agree. That question illustrates the strong conservative shift within the Republican party. In the final years of the Reagan administration, 62% of Republicans agreed on the need for a safety net.

Similarly, although members of both parties express skepticism about how well government regulation of business works, 80% of Democrats say that a “free market economy needs regulation to serve the public interest.” Republicans are evenly divided on that question. Tea party Republicans by a 2-1 majority reject the idea that regulation is needed.

When Pew first began its surveys, Americans’ views about the environment showed no significant partisan divide -- nearly 90% of Democrats, independents and Republicans agreed on a need for “stricter laws and regulations to protect the environment.” Today, after several decades of increasing environmental regulation, a huge, 46-point partisan gap exists on that question. Democrats’ views on the need for more regulation have remained steady, and independents have shifted a relatively small amount. Republican support for further environmental regulation has plummeted: 47% now say yes.

Those three questions illustrate how a conservative shift among Republicans has widened the partisan gap. On other issues, shifts to the left by Democrats have been the major force for greater division.

While the Republicans overwhelmingly are a party of white conservatives -- 87% of self-identified Republicans are white, and 68% are conservatives -- the Democrats have become a coalition heavily based on minorities and white liberals. The number of Democrats calling themselves liberal now equals the number who identify as moderate -- 38% each.

One result of the racial gap between the parties shows up in a question about whether “blacks and other minorities” should be given “preferential treatment” to improve their position. Majorities of both parties used to say no to that, and Republicans continue to do so overwhelmingly. But among Democrats, 52% now say yes.

Views on immigration and immigrants show a similar pattern. A decade ago, about half the adherents of both parties said that immigrants “threaten traditional American customs and values.” Today, 60% of Republicans express that view, but among Democrats, the number has dropped to 40%.

The Democratic shift has come in part because Latinos have become a greater share of Democrats, and very few of them see immigrants as a threat. But the views of whites also have changed, with only 14% of white liberals saying they see immigrants as a threat. Blacks are far more likely to see immigrants as threatening.

Democrats also have become more secular. The number of Democrats saying they sometimes doubt the existence of God has increased, although large majorities in both parties still say they never experience such doubts.

As both parties have become more ideologically consistent -- Democrats to the left, Republicans to the right -- both have lost supporters, and the percentage of Americans identifying themselves as independents has increased. But most of those self-identified independents lean one way or the other, and their views closely align with those of avowed partisans, the study found.

Including those independents who lean one way or the other, Pew found 48% of adults supported the Democrats and 40% the Republicans. The relatively small group that did not lean either way stood out mostly for their disengagement from politics.

david.lauter@latimes.com