IN a partisan country locked in a polarizing campaign, there is no shortage of much discussed divisions: religious and secular, the 99 percent and the 1 percent, red America and blue America.

But you can make a strong case that one dividing line has actually received too little attention. It’s the line between young and old.

Draw it at the age of 65, 50 or 40. Wherever the line is, the people on either side of it end up looking very different, both economically and politically. The generation gap may not be a pop culture staple, as it was in the 1960s, but it is probably wider than it has been at any time since then.

Throughout the 1980s and ’90s, younger and older adults voted in largely similar ways, with a majority of each supporting the winner in every presidential election. Sometime around 2004, though, older voters began moving right, while younger voters shifted left. This year, polls suggest that Mitt Romney will win a landslide among the over-65 crowd and that President Obama will do likewise among those under 40.

Beyond political parties, the two have different views on many of the biggest questions before the country. The young not only favor gay marriage and school funding more strongly; they are also notably less religious, more positive toward immigrants, less hostile to Social Security cuts and military cuts and more optimistic about the country’s future. They are both more open to change and more confident that life in the United States will remain good.

Their optimism is especially striking in the context of their economic troubles. Older Americans have obviously suffered in recent years, with many now fearing a significantly diminished retirement. But the economic slump of the last decade — a mediocre expansion, followed by a terrible downturn — has still taken a much higher toll on the young. Less established in their working lives, they have struggled to get hired and to hold on to jobs.

The wealth gap between households headed by someone over 65 and those headed by someone under 35 is wider than at any point since the Federal Reserve Board began keeping consistent data in 1989. The gap in homeownership is the largest since Census Bureau data began in 1982. The income gap is also at a recorded high; median inflation-adjusted income for households headed by people between 25 and 34 has dropped 11 percent in the last decade while remaining essentially unchanged for the 55-to-64 age group.

If there is a theme unifying these economic and political trends, in fact, it is that the young are generally losing out to the old. On a different subject, Warren E. Buffett, 81, has joked that there really is a class war in this country — and that his class is winning it. He could say the same about a generational war.

Younger adults are faring worse in the private sector and, in large part because they have less political power, have a less generous safety net beneath them. Older Americans vote at higher rates and are better organized. There is no American Association of Non-Retired Persons. “Pell grants,” notes the political scientist Kay Lehman Schlozman, “have never been called the third rail of American politics.”

Over all, more than 50 percent of federal benefits flow to the 13 percent of the population over 65. Some of these benefits come from Social Security, which many people pay for over the course of their working lives. But a large chunk comes through Medicare, and contrary to widespread perception, most Americans do not come close to paying for their own Medicare benefits through payroll taxes. Medicare, in addition to being the largest source of the country’s projected budget deficits, is a transfer program from young to old.

Meanwhile, education spending — the area that the young say should be cut the least, polls show — is taking deep cuts. The young also want the government to take action to slow global warming; Congress shows no signs of doing so. Even on same-sex marriage, where public opinion is moving toward youthful opinion, all 31 states that have held referendums on the matter have voted against same-sex marriage.

Over the long term, obviously, the young have a distinct advantage: they’re not going away. So one of the central questions for the future of American politics is whether today’s 20- and 30-year-olds will hold on to many of the opinions they have today, a pattern that would be less surprising than glib clichés about aging and conservatism suggest. Until recently, as the presidential results from the 1970s through the 1990s make clear, Americans did not grow much more conservative as they aged.

And while today’s young are not down-the-line liberal — they favor private accounts for Social Security and have reservations about government actions to protect online privacy — they certainly lean left.

No one knows exactly why, but there are some suspects. Having grown up surrounded by diversity, they are socially liberal, almost unconsciously so. Many of them also came of age in the (ultimately unpopular) George W. Bush presidency, or the (ultimately popular) Bill Clinton presidency, and pollsters at the Pew Research Center argue that the president during a generation’s formative years casts a long shadow, for better or worse. Hammered by the economic downturn, young voters say they want government to play a significant role in the economy.

These attitudes create a challenge for the Republican Party that is arguably as big as its better known struggles for the votes of Latinos. “We’ve got a generation of young people who are more socially liberal and more open to activist government,” says Andrew Kohut, president of the Pew center, which has done some of the most extensive generational polling. “They are quite distinct.”

Shortly after Mr. Bush won re-election in 2004, just when the age gap was emerging, his chief campaign strategist, Matthew Dowd, wrote a memo to other top Bush aides urging them not to assume that a new Republican majority was emerging. The exit polls, he wrote to Karl Rove and others, showed that younger voters had voted strongly Democratic, and those voters would be in the electorate for a long time to come.

“They don’t think the Republican Party thinks like them,” much as older voters feel alienated by what they see as today’s immigrant-embracing, gay-friendly, activist-government Democratic Party, Mr. Dowd said last week. “I don’t expect these younger voters to wake up all of a sudden when they’re 38 years old and say, ‘I was for gay marriage before, but now I’m against it.’ ”

Still, it would be mistake to assume that today’s young are going to be Democrats for life. Many children of the 1960s, after all, grew up to be Ronald Reagan voters. The political landscape shifts over time. Frustrated by a weak economy and a government that disproportionately benefits the old, younger adults could become ever more reluctant to send tax dollars to Washington. The Republican Party could grow more libertarian and thus more in line with the social views of the young.

What seems clear is that the marketing gurus are finally right: today’s young really are different. They view a boisterously diverse United States as a fact of life, and they view life as clearly better than it used to be. But they are also products of the longest economic slump in 70 years, and they would like a little help. They wish the country would devote more attention to its future, especially on education and the climate. They, of course, will have to live with that future.

David Leonhardt is the Washington bureau chief of The New York Times.