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Peculiarities of the 2004 campaign might also have maximized Mr. Kerry's performance among young voters. The Democratic get-out-the-vote effort placed heavy emphasis on the youth vote, employing pop-cultural icons and exploiting the fear of a military draft. The strong youth vote for Kerry may prove to have been less a trend than a spike.

Peculiarities of the 2004 campaign might also have maximized Mr. Kerry's performance among young voters. The Democratic get-out-the-vote effort placed heavy emphasis on the youth vote, employing pop-cultural icons and exploiting the fear of a military draft. The strong youth vote for Kerry may prove to have been less a trend than a spike.

While the Roe effect may give Republicans an advantage, it obviously is insufficient to win elections. National security and the economy still loom larger than abortion in most voters' minds. And although no Democratic candidate since 1976 has won a popular-vote majority, pro-choice candidates collectively (including Ross Perot and Ralph Nader) did so in the three elections from 1992 to 2000. Further, the Roe effect does not necessarily mean that younger voters will end up conservative on cultural issues other than abortion. Opinion polls consistently show, for example, that the young are far more favorable toward same-sex marriage than their elders. This should not be surprising. Even if their parents tend to be conservative, they grew up in a society far more accepting of homosexuality than the one in which earlier generations came of age.

While the Roe effect may give Republicans an advantage, it obviously is insufficient to win elections. National security and the economy still loom larger than abortion in most voters' minds. And although no Democratic candidate since 1976 has won a popular-vote majority, pro-choice candidates collectively (including Ross Perot and Ralph Nader) did so in the three elections from 1992 to 2000. Further, the Roe effect does not necessarily mean that younger voters will end up conservative on cultural issues other than abortion. Opinion polls consistently show, for example, that the young are far more favorable toward same-sex marriage than their elders. This should not be surprising. Even if their parents tend to be conservative, they grew up in a society far more accepting of homosexuality than the one in which earlier generations came of age.  It should also be noted that immigration, particularly by Hispanics, could dampen the Roe effect if, as is probable, they are more likely to vote for a Democratic candidate than a Republican one.

And if Republicans keep winning the presidency and appointing Supreme Court justices, ''Roe v. Wade'' may eventually be overturned. If ''Roe'' goes by the boards, one would expect fertility to increase in states that outlawed abortion, which would presumably be largely conservative and Republican ones. If the Roe effect continues to operate, though, it would make those states more Democratic and liberal, since women who otherwise might get abortions would no longer have the option in their home states. But in the end, that may not matter. If ''Roe'' were overturned, the politics of abortion would change dramatically, and in the Democrats' favor. With the legality of abortion itself on the line, the debate would shift away from the pro-choice extremes, forcing pro-choice politicians to take a more centrist (and popular) position. Republicans would be torn between their antiabortion base and more moderate voters, for whom an outright ban on abortion is a bridge too far.

And if Republicans keep winning the presidency and appointing Supreme Court justices, ''Roe v. Wade'' may eventually be overturned. If ''Roe'' goes by the boards, one would expect fertility to increase in states that outlawed abortion, which would presumably be largely conservative and Republican ones. If the Roe effect continues to operate, though, it would make those states more Democratic and liberal, since women who otherwise might get abortions would no longer have the option in their home states. But in the end, that may not matter. If ''Roe'' were overturned, the politics of abortion would change dramatically, and in the Democrats' favor. With the legality of abortion itself on the line, the debate would shift away from the pro-choice extremes, forcing pro-choice politicians to take a more centrist (and popular) position. Republicans would be torn between their antiabortion base and more moderate voters, for whom an outright ban on abortion is a bridge too far.