WASHINGTON – The political paralysis in Washington is often ascribed, depending on partisanship, to Republican obstructionism or President Obama’s arrogance. But there are deeper causes to the stalemate.

Both parties have had a hard time creating agendas that appeal across ideological, racial and ethnic lines. There’s been a fragmentation of power and purpose that transcends the defects of political leaders.

A partial explanation comes in a significant report issued last week that describes the changing nature of the American electorate. It’s less white, more minority, older and less dominated by any one generation. Fascinating in their own right, these shifts also illuminate the larger origins of the political impasse. If democracy is responsive to voters, then voters preoccupied with their own narrow agendas inhibit the creation of durable coalitions capable of legislating.

The report, “States of Change: The Demographic Evolution of the American Electorate, 1974-2060,” was sponsored by three think tanks of differing politics: the conservative American Enterprise Institute; and the liberal Brookings Institution and Center for American Progress. The study identifies 10 transforming trends, which – considering the overlap – I’ve condensed to five.

Here they are:

1) The rise of minorities – and decline of whites. In 1980, 80 percent of the U.S. population was white. Now, that’s 63 percent; by 2060, it’s projected to be about 44 percent. Meanwhile, Hispanics have gone from 6 percent in 1980 to 17 percent now and are projected to reach 29 percent by 2060. Asian-Americans (and “others”) are expected to double from 8 percent now to 15 percent by 2060. African-Americans, now 12 percent to 13 percent, are estimated to stay stable.

2) A graying America. People 50 and older now represent one-third of the population, up from one-fourth in 1980. By 2060, their share is forecast to exceed two-fifths. By contrast, those 18 to 39 are then expected to be about a quarter of the total.

3) Generational shifts. These are inevitable, of course. The World War II generation is mostly gone (it’s 1 percent of the population). And baby boomers, born from 1946 to 1964, no longer dominate. They’re 24 percent of today’s population, slightly behind “millennials,” born from 1981 to 2000, at 27 percent, and slightly ahead of Generation X, born from 1965 to 1980, at 21 percent. (The remaining population consists of the young and the very old.)

4) The rise of unmarried voters. This is perhaps the most surprising finding. In 1974, 70 percent of eligible voters were married, 30 percent unmarried. Now, the split is 52 percent married, 48 percent not, reflecting fewer and later marriages, more divorces and more widowed elderly.

5) The gap between voters and the population. In 2012, slightly more than one-fourth of actual voters were minorities – well below their population share of about 37 percent. The reasons are clear. Many immigrants aren’t eligible, either because they’re children or not citizens. Also, turnout is low among eligible voters. With time, this gap should close.

None of these groups, of course, is a political monolith. But if power ultimately derives from the people, then these changes are not just electoral curiosities. They condition how the system operates. Power is being redistributed in ways that breed widespread dissatisfaction. As a group, whites still have the most power, but it is waning. Hispanics’ power is on the rise, but it has been (so far) insufficient to pass desired immigration legislation.

Crafting political campaigns that resonate with most of the population has become harder. Helping married couples (with, say, a new tax break) may offend the equally large pool of unmarried. Baby boomers may be able to defend their Social Security and Medicare benefits, but their good fortune is partially paid by taxes on struggling millennials.

The “next America” – to borrow writer Paul Taylor’s phrase and the title of his book – has arrived, and its beginning is not auspicious. Both parties are struggling to find themes that bridge differences. “Middle-class economics” is Democrats’ latest effort.

To be sure, this next America is hardly fixed. Time passes; social and political realities shift. At a conference on the report, Elaine Kamarck of the Brookings Institution sensibly wondered whether the children and grandchildren of todays’ immigrants will continue to identify themselves as Hispanic. “As people intermarry, will it matter that the United States is a majority/minority society?” she asked. It may not.

But some things don’t change. The central problem of American governance, dating back to the design of the Constitution, is how to create a political system that advances the nation’s long-term interests even though politics is dominated by groups (including states and localities) avidly pursuing their short-term self-interests. Power may derive from the people, but it must be tempered in ways that allow for the future. This is a challenge every generation faces – and one that we are arguably failing.

Robert Samuelson is a columnist for The Washington Post. © 2014 The Washington Post Writers Group.