Maybe the Tea Party isn't the real threat to the Democrats after all. The greatest threat to the Democratic majorities in Congress just may be old people.

Margaret Talev points out that older voters—a group that once largely voted Democrat—are increasingly voting Republican. That's because the number of seniors who came of age under FDR is dwindling, while there are still relatively few seniors who came of age under JFK. More older Americans today are Eisenhower Republicans, who cast their formative first votes in the more conservative 1950s. Most seniors voted for John McCain in the last election. When asked which party they would vote for if the 2010 election were held today, Americans are fairly closely split between Republicans and Democrats. But the latest GWU Battleground poll finds that older voters favor the Republicans by a margin of 48-31, making them about 7 percentage points more conservative that the average voter.

As Talev says, passing health care reform only made matters worse for the Democrats. The same poll finds that older voters oppose the new law by a margin of 58-36, more than any other age group. Health care reform, obviously, doesn't benefit seniors—who are already covered by Medicare—as directly as it does younger voters. And the accusation that the bill would mean the creation of "death panels"—as absurd as it was—appears to have turned some older people against the law.

That's why President Obama and the Democrats are so focused on getting out the youth vote in the fall. The problem for them is that young people—who turned out in droves to help vote Obama into office—typically don't vote in midterm elections. Without a presidential campaign to draw them to the polls, they are unlikely to vote in large numbers this fall either. A recent Gallup poll found that people over 65 were twice as likely as people between the ages of 18-29 to say they were "very enthusiastic" about voting in November's congressional elections. And almost half of people 18-29—who favor the Democrats by a large margin—said they weren't enthusiastic about voting in the fall at all. That won't help the Republicans retake the presidency in 2012. But it's one reason why things look bad for the Democrats this fall.