Now it must be said that of course Facebook is not trying to elect Democrats. Facebook has an admirable civic virtue and has long tried to increase democratic participation in a strictly nonpartisan way. "Facebook," Fowler said to me, "wants everyone to be more likely to vote. Facebook wants everyone to participate in the fact of democracy."

But that doesn't mean the effects of Facebook's efforts are not lopsided. Outside of Facebook's demographic particularities, there are reasons to believe that improved voter turnout in general helps Democrats, though there is a debate about this within political science.

In practice, though, there is no such thing as pure a get-out-the-vote, one whose tide raises all votes, and Facebook is no exception. It skews toward both women and younger voters, two groups which tended to prefer Democrats on Tuesday. Eighteen-to-29-year-olds voted 60 percent for Obama, compared with 37 percent for Romney. The next-older age group, 30-to-44-year-olds, gave Obama 52 percent of their support. Among Americans older than 45, Romney won. The implication is clear: If Facebook provides a cheap and effective way to get more people to the polls, and it seems that it does, that is good news for Democrats. For Republicans, well, it's an uncomfortable situation when increasing voter participation is a losing strategy.

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Facebook's effect -- however big it is -- is at the margins, and in a country where elections are so close, the margins can matter a lot. But there are long-term trends underfoot that, for Republicans, mean their troubles go beyond Facebook. This year was the third presidential election in a row where young-voter participation hovered around 50 percent (meaning that half of eligible young people actually voted), Peter Levine of the Center for Information and Research on Civic Learning and Engagement at Tufts University told me, and this is up from a low of just 37 percent in 1996. Obviously, that sort of shift is not the result of a Facebook message. "This seems to be a significant generational change," he said.

The reasons for this generational change are complex and not totally understood. One certain factor is simply that recent campaigns have tried harder to reach out to young people. "In the 1990s the conventional wisdom was that young people don't vote," Levine said. "So they would literally look through a contact list of potential voters to reach out to, and just delete the young people -- not to discriminate but because they were trying to be efficient."

"In the 1990s the conventional wisdom was that young people don't vote," Levine said. "So they would literally look through a contact list of potential voters to reach out to, and just delete the young people."

But that ended with what Levine calls the "50/50 nation situation" -- elections so close that campaigns could no longer afford to write off huge parts of the population. "It had already begun to change, but Obama won on the strength of young votes in '08 -- not only in the general election but especially in the primaries. They gave him Iowa. Without Iowa, no President Obama."