Hillary Clinton and Sarah Palin have helped draw unprecedented attention to female voters this year. But what will men do at the ballot box on Nov. 4? And how many of them will bother to show up at all?

Over the last 40 years, some 16 million men—a population roughly the size of Michigan and Indiana combined—have stopped pulling the lever. That's a hole five times the size of George W. Bush's margin of victory in 2004. How did it get so bad? Since 1964, when a record 72 percent of voting-age men and 67 percent of voting-age women pulled the lever for president, participation rates have tumbled for both sexes—but far more steeply for men. By 1980, civics-class dropouts had flipped the gender gap. And this November, men are again the odds-on favorites to no-show at the polls.

"Unless there is an astonishing reversal of a 30-year trend," says New York University professor Rogan Kersh, an expert on voting patterns, "far fewer men than women will show up this year, both in real terms and a percentage of their gender."

Other social scientists echo Kersh, although the exact date that men fell behind differs according to how one does the counting. Data that includes all residents over age 18 finds the pivotal year to have been 1980, while figures that exclude felons and legal immigrants—groups that are disproportionately male—date it to 2004. Both formulas reveal curdling male involvement over time. "It's been a gradual but persistent separation," says Harvard University's Thomas Patterson, author of "The Vanishing Voter."

Some politicos say that the Democratic Party has suffered the most from the male malaise, since its base of white working-class men has been eroding. But the shift cuts against the GOP, too. Strong female majorities and subpar male turnout helped elect Bill Clinton to two terms. This election, the missing male vote could sink McCain, whose choice of Palin as a running mate may end up backfiring. A Pew poll late last month found that 53 percent of men have a favorable opinion of Palin—4 points higher than women. Meanwhile, Barack Obama is going where the boys are: his campaign has bought ad space on virtual billboards in videogames like John Madden Football, NBA Live and Grand Theft Auto.

Apathy, anger and inattentiveness have all contributed to a decline in voting among both genders. But some factors are almost exclusively a guy thing.