This is turning into a tough election year for Democrats, and most of the reasons are familiar: The economy is stalled, President Obama's popularity is sagging and voters are in an anti-incumbent mood. There's an "enthusiasm gap" too. Republican voters are fired up and ready to vote, while liberals are dispirited.
Now add one more factor: a new generation gap. Voters over the age of 50 are leaning increasingly Republican, according to recent polling - and that includes members of the giant baby boom generation between 50 and 64.
A Pew Research poll released last week found that most voters over 50 say they favor the Republicans in November's congressional election. Voters in their 30s and 40s were evenly split; voters younger than 30 favored the Democrats. That's a big problem for Democrats, in two ways.
First, older voters are a bloc the party doesn't want to lose. They turn out on Election Day more consistently than younger voters - especially in a non-presidential election, like this year's. About two-thirds of November's voters will be 50 or older.
Second, the defections may reflect a deeper, longer-term trend: The baby boom generation appears to be growing more conservative as it ages.
Democrats already knew they had trouble with voters over the age of 65. Those voters - the true senior citizens - were the only age group that John McCain carried in the presidential election of 2008.
But the baby boomers - the cohort from 50 to 64 - had been in the Democrats' grasp. Boomers voted for Obama in 2008. They voted strongly for Democrats in the congressional election of 2006. (They voted for George W. Bush in 2004, but only by a narrow margin - unlike the more conservative 65-plus voters.)
Now, though, many of the boomers who voted for Obama are moving into the Republican column - and behaving (or at least answering survey questions) just like the older cohort.
"There's evidence that those two generations, the early boomers and the seniors, may be converging," said Andrew Kohut, Pew's director. "If it holds up - and we'll see in November - that could be a significant change."
Those "early boomers," born between 1946 and 1960, reached adulthood in the 1960s and '70s - the era of the Vietnam War and the counterculture. According to one prevailing theory of voter behavior, their first political experiences should have stamped them for life. They started out voting mostly for Democrats; they helped elect one of their own, Bill Clinton, to two terms in the White House.
Why are they moving? One answer, political strategists from both parties say, is that older voters are worried - about the economy, the federal deficit and the prospect of rising taxes. And as they age, they're worried that Obama's health-care law could harm Medicare, even though the president has promised it won't.
Polls taken during the healthcare debate last year found that senior citizens over 65 were more strongly opposed to the plan than any other age group - but over time, they were joined by middle-age baby boomers, who became increasingly negative.
"Older voters are worried that the quality of their healthcare could decline," said David Winston, a Republican pollster. "That opens a door where they're willing to listen to Republicans. It's a huge opportunity."
Republicans are seizing it by casting themselves as defenders of Medicare, a Democratic initiative their party once opposed. They're charging that $523 million in Medicare spending cuts under the new law will hurt medical care for senior citizens.
Obama and his aides are fighting back, of course. They plan to spend much of the summer promoting more popular aspects of the health-care law, including the $250 checks they began mailing in June to Medicare patients who fall into the "doughnut hole" limit on drug benefits. They've even enlisted allies outside the government to raise $125 million for a campaign to promote the health-care reform package. Polls show that the law's popularity is slowly inching upward - but not among most older voters yet.
And health care is merely this year's battle. If those millions of baby boomers continue drifting rightward, Democrats will have a problem that extends well beyond November's congressional election.
"There's a long-running debate," noted Democratic pollster Mark Mellman. "Are political views a product of voters' generational experience or of their place in the life cycle?
"To the extent that it's a product of their place in the life cycle, (older voters) are beginning to look a lot like their parents," he said. "They are becoming more conservative over time - more conservative on economic issues but more liberal than their parents on social issues."
Which leaves Democrats with two options for responding to the shifting generational wind. One is to trim their sails - to chart a more conservative course and respond to aging voters' fears about healthcare and taxes and the deficit. (Some are trying to do that now.) The other is to rely on the passage of time - to wait for an influx of younger people and minority voters to change the electorate in their direction. That might work, but not by this November.
Of course, the Republicans have problems too. But that's for another column - coming soon.
Doyle McManus is a columnist for The Los Angeles Times. Readers may send him e-mail at email@example.com.