WASHINGTON — American politics has long been defined as Red vs. Blue, and everything about the 2012 election speaks to the chasm that separates the two parties. But a major new study highlights how those divisions are only a part of the dynamic shaping the political landscape.

The study, conducted by The Washington Post and the Kaiser Family Foundation, underscores that the gulf between Republicans and Democrats has never been wider. Partisan polarization now presents a potentially insurmountable barrier to governing for whomever wins the White House in November.

But the study — based on a poll of more than 3,000 randomly selected adults — also illuminates in striking new ways another reality about the contours of politics. Like families, the parties coalesce to repel threats from outside — typified this summer by the scorched-earth tactics of the campaigns of President Barack Obama and Republican Mitt Romney. But both parties also are fractious coalitions of people who may converge on some core issues but whose worldviews, economic situations and attitudes on policy are far from uniform.

These disparate and ever-evolving coalitions present challenges for both Obama and Romney. They are why Romney struggled through much of the Republican nominating contest to win over key parts of his party and only united the GOP coalition by picking Rep. Paul Ryan, R-Wis., as his vice presidential running mate. It is why Obama has faced dissonance and disappointment over the way he has governed from some elements of the Democratic Party, particularly many liberals who nonetheless back him strongly for reelection.

The two major parties will be on display over the coming weeks at their national conventions. Republicans go first, starting Aug. 27 in Tampa. Democrats meet in Charlotte the following week. Both will try to project an image of unity as they draw distinctions with their opponents. But Romney’s selection of Ryan is a reminder that the parties recognize success in November depends in part on keeping their coalitions together and energized.

The Post-Kaiser survey examined the breadth and diversity of the electorate to explore the changing shape of a Republican coalition that has become more Southern in its base and more conservative in its views, and yet encompasses which significant disagreements remain over whether confrontation or cooperation with the Democrats is the preferred path for governing.

The study looks, too, at a Democratic Party that, while women make up a clear majority of supporters and grassroots activists have a large voice, is a coalition of groups with divergent views on government regulation of the economy, the size of government, the role of religion in public life and such hot-button social issues as abortion and same-sex marriage.

This article focuses on those Americans who, when asked, say they identify with either the Republican or Democratic Party. A later article will look at those Americans who call themselves independent — a fast-growing part of the electorate — and explore the question of just how independent they really are.

In some ways, political parties matter less than they once did, but party identification is one of the most reliable indicators of how someone will vote on Election Day. The Post-Kaiser study breaks down the two parties into nine groups of voters: five groups who call themselves Republicans and four who call themselves Democrats.

Examined in this way, the fissures within the Republican and Democratic coalitions are more sharply etched. One can see elements of the Republican Party of a generation ago in Republicans who are economically conservative but socially moderate. One can also see the new Republican Party in those Americans who strongly identify with the tea party movement or are evangelical Christians who came to prominence in the party over the past two decades. There is even a group of Republicans who see a role for bigger government — at least a bigger role than others in the party accept.

The Democratic coalition includes a large share of liberal, affluent and mostly secular white voters but also a loyal cadre of African Americans and Latinos who are more religious and more conservative on social issues. The gap between them on social issues remains wide, but they are generally united in advocating a significant role for government.

The survey speaks to the two realities of political life — each party bound together in opposition to the other at the same time both continue to squabble internally. This article will first look at the divisions between the parties, which are reflected daily in the presidential campaign debate and which have defined the battles between the president and congressional Republicans during Obama’s first term. Then it will describe the internal tensions of each of those parties.

Partisan polarization once was considered an affliction only of elected officials and political elites. Now it has gone mainstream. Citizens’ ties to their political parties are stronger than ever, and passions on issues are intensely felt.

Fourteen years ago, The Post, along with the Kaiser Family Foundation and Harvard University, asked people to assess the strength of their allegiance to the parties. At that time, 41 percent of Republicans and 45 percent of Democrats said they considered themselves “strong” partisans. In the new Post-Kaiser survey, those numbers have shot up to 65 and 62 percent, respectively.

Over this time period, the gap between Democrats and Republicans has widened, particularly when it comes to attitudes about the federal government. A clear majority of Republicans now score highly on a series of questions about limited government. That was not the case in 1998. Also unlike in 1998, a majority of Democrats in the new survey cluster on the other end of the scale.

One set of answers is particularly revealing: The number of Republicans who feel strongly that the government controls too much of daily life jumped 24 percentage points since the 1998 survey, to 63 percent. The number of Democrats strongly disagreeing with the assertion doubled.

The debates during Obama’s presidency over health care, economic stimulus and financial regulatory reform underscore how far apart the parties stand on economic issues and on attitudes about government’s role. For example, more than twice as many Democrats as Republicans say regulation of business is necessary to protect the public interest. Most Republicans say regulation does more harm than good.

The two parties are miles apart on whether it is better to have smaller government with fewer services or bigger government with more services. Republicans overwhelmingly say people should take care of themselves; Democrats overwhelmingly say government should do everything possible to improve living standards.

Republicans see deficit reduction as more important than spending money in an effort to create jobs. Democrats believe the opposite.

Divisions over religious and social issues are equally stark. As a whole, the two parties are mirror images of each other on whether organized religious groups should stay out of politics or stand up for their beliefs in the political arena. They are similarly at odds over whether there should be a high wall of separation between church and state and whether government should more actively protect religious heritage.

Both parties contain deeply observant people as well as many who seldom go to church or synagogue or mosque. But in general, a higher percentage of Republicans, by far, are frequent churchgoers. One of the fastest-growing segments of the Democratic Party in recent years has been nonbelievers or infrequent churchgoers.

Big majorities in both parties see tolerance of other’s lifestyles as important, but Republicans and Democrats take opposite positions on whether changing mores should affect personal convictions. A majority of Democrats agree with the proposition that as the world changes, people should adjust their morals and values. An even bigger majority of Republicans disagree with that statement, with most saying so strongly. Far more Republicans than Democrats say Americans in general are too tolerant of behavior that once was considered wrong or immoral.

On abortion and gay marriage, the divide between the parties is wide. Twice as many Democrats as Republicans say abortion should be legal in all or most cases. The margin between the parties is similarly gaping when it comes to same-sex marriage.

Recent shootings in Colorado and Wisconsin have sparked renewed discussion about gun laws. Over the past two decades, overall support for new restrictions has declined, to the point that today barely more than half of those surveyed favored stricter laws. Republicans overwhelmingly oppose tougher restrictions. Democrats overwhelmingly favor tougher laws, but the president and other party leaders are reluctant to propose them.

On some issues, partisan divisions have blocked action in Congress, but the Post-Kaiser study shows that rank-and-file Republicans and Democrats are less divided.

Take immigration, for example. Almost half of Republicans and three-quarters of Democrats say they favor a policy that would allow illegal immigrants to apply for legal status. And six in 10 Republicans, along with almost nine in 10 Democrats, say the government should regulate the release of greenhouse gases from power plants, cars and factories to reduce global warming.

There is also consensus on two international issues. Few in each party say the United States should play the leading role in the world. More say this country should play a major but not leading role, and around a quarter in each party would prefer the United States to play a minor role. This is an example of an area where Romney, who prefaced his overseas trip with a speech in which he said it is essential for the United States to play the lead role, is out of step with rank-and-file Republicans.

On the trade-off between fighting terrorism and protecting civil liberties, big majorities in both parties say the government is doing enough to protect the liberties of individual citizens. Five years ago, the country was evenly divided on that question, with Democrats far more worried about civil liberties.

Another key area where Republicans and Democrats see the world the same way, though from totally different perspectives, is a shared sense of being at risk of losing what they have. Almost identical percentages — around six in 10 in each party — say groups and people who hold values similar to theirs are losing influence in American life.

Given that, is there any wonder the presidential campaign is being fought as if it were a life-and-death struggle politically?

What does it mean to be a Republican in 2012? Republicans are conservative, opposed to big government, overwhelmingly white and spread through all regions, although with a heavy concentration in the South. At least that’s the case on the surface.

Fault lines lie beneath, revealed in primary election battles between tea party conservatives and more establishment politicians and tensions that pit economic conservatives against religious and social conservatives.

Party types

The Post-Kaiser analysis reveals five distinct types of Republicans. Four are familiar elements of the GOP coalition: “Tea Party Movement Republicans,” “Old-School Republicans,” “Religious Values Voters” and “Pro-Government Republicans.” The fifth, a group we label “Window Shoppers,” are self-identified Republicans who in many respects seem out of place in an increasingly conservative party.

There are demographic differences among the groups. The party is about evenly split between men and women, but women make up a solid majority of Values Voters, while men make up about six in 10 Old-School Republicans.

Republican identifiers are overwhelmingly white, but two groups — Pro-Government conservatives and Window Shoppers — include significant numbers of nonwhites. Window Shoppers, the category that is least likely to agree with other groups within the party on many issues, are by far the youngest group: four in 10 are under age 30.

Old-School Republicans generally have higher incomes and more formal education. More than two-thirds of those in the Pro-Government group have annual household incomes of less than $50,000 and do not have college degrees.

Big majorities of the Pro-Government, Tea Party Movement and Values Voters groups attend religious services weekly; few Window Shoppers and Old-School Republicans go to church that regularly. There also are stark differences when it comes to attitudes about the role religion should play in public life.

Underlying demographic and behavioral differences lead to conflicting attitudes and values on many issues. Pro-Government and Old-School Republicans are less inclined to say GOP leaders are taking the party in the right direction, while the Tea Party Movement and Values Voters groups are much more satisfied.

Most Republican groups favor confrontation over cooperation and compromise, but Old-School Republicans and Window Shoppers tend to favor negotiation with the Democrats.

Almost all Tea Party Movement and Old-School Republicans say people should take care of themselves and not look to government for help, a sentiment that drops sharply among Pro-Government conservatives.

On Medicare, an issue central to the presidential campaign, the Republican coalition is divided. The survey asked everyone whether they preferred changing Medicare to a premium-support program for younger workers, in which people would have the option to purchase their own health-care plans after retiring, an idea Ryan has outlined and Romney has embraced. Or, they were asked, would they prefer to keep the government health program largely as it is?

Tea Party Movement Republicans were the only one of the five GOP groups in which a majority favored the premium-support approach advocated by Ryan. About four in 10 Old-School Republicans said they supported such a change. But more than 60 percent of those in each of the other groups said they opposed the idea.

Old-School Republicans, who once were called country-club Republicans, tend to be out of step with others in the party on a variety of social issues: A slim majority say same-sex marriages should be legal, and more than a third say people’s values should adapt to changing times and cultures. These Republicans, along with the Window Shoppers, score no higher on a scale of “moral relativism” than do two of the major Democratic groups.

The GOP is now a collection of shifting internal coalitions. For the next three months, they will join together in a united effort to defeat Obama, capture the Senate and enlarge their majority in the House. But if Romney is in the White House come January, he will be faced with harnessing a party that in a variety of ways will be pulling in different directions, substantively and stylistically.

Obama’s election-year announcements on gay marriage and a naturalization policy for undocumented immigrants seemed to play to a Democratic base, one that is largely supportive of his moves. Democrats certainly differ from Republicans on the issues, at least broadly.

But Democrats too are divided — particularly on gay marriage.

Fully 85 percent of those we call “Urban Liberals” — one of the biggest of the Democratic groups — say they feel strongly that gay marriage should be legal, but that drops to 26 percent among “God and Government” Democrats, the largest group, and just 13 percent among the smallest cadre, the do-it-yourself, or “DIY,” Democrats.

Religion, social issues and the size and scope of government are the main pivots dividing the Democratic coalition, but demographic differences also contribute to the fissures.

Urban Liberals — the most traditionally liberal of the groups — are nearly three-quarters white and by far the most educated and highest income earners among Democrats. The God and Government contingent is two-thirds nonwhite and far more apt than two of the five Republican groups to go to religious services at least once a week.

Urban Liberals and the “Agnostic Left,” another group of people who seldom go to church, overwhelmingly say there should be a high degree of separation between church and state, while sizable majorities of the other two groups of Democrats say the government should take special steps to protect America’s religious heritage.

About a third of DIY Democrats advocate a larger federal government offering more in services, a position backed by most of those in other groups, peaking at 85 percent among Urban Liberals. DIY Democrats are by far the least likely of any of the four groups to support new spending at the cost of deficit reduction. But they also represent only about one in eight Democrats — only about a third of the size of the God and Government group.

The Agnostic Left, about two-thirds of whose members are under 50 years old, nearly matches the DIY group in its overall espousal of economic individualism but differs sharply when it comes to issues around religion’s role in public life.

Obama has been able to stitch together a unique coalition, still reliant on a nonwhite base but reaching into some segments of voters previously resistant to Democratic presidential candidates. But the near uniformity in Democrats’ intentions to support his bid for reelection belies deep disagreements that are likely to color the remainder of his presidency, whether he has five months or another four years in office.