His And Hers Politics

A recent Quinnipiac poll found that Obama has an 18-point lead among female voters. Pamela Haag tracks the history of the gender gap as "an artifact of post-Roe politics": 

In the early 1900s suffragettes predicted that granting women the vote would transform American electoral politics, but voting patterns before the 1970s didn’t actually reveal women’s footprint as a distinct voting bloc. Men and women had fairly similar voting patterns. The gender gap didn’t register in the Carter-Ford contest of 1976, either, in which Carter got 50 percent of the votes of both men and women.

But in 1980, a relatively modest “gender gap” emerged (the Rutgers Center for American Women and Politics has a useful summary of the historical trends). A victorious Ronald Reagan got 46% of the women’s vote, but 54% of the men’s vote, for an 8-point gender gap in his support. He had a slightly smaller, 6-point gap in his 1984 re-election.

It's zig-zagged since then:

It dipped as low as a 4-point advantage in the 1992 election, when President Clinton got 45% of the women’s vote to 41% of the men’s vote, and reached its heretofore widest point in Clinton’s 1996 re-election, where he won 54% of women compared to 43% of men, for an 11-point difference. From 1996 on, however, the gender gap had actually been closing somewhat. It was smaller in the Bush-Gore contest (10 points), smaller still with Bush-Kerry (7 points), and remained at 7 points in the 2008 Obama-McCain campaign.

That context makes Romney’s stunning deficit among women in this campaign all the more notable.

M.D. at Democracy in America argues that the oft-cited trend of women migrating leftward misses something crucial:

[A] look at the trend in party identification among women and men indicates that the source of the gender gap is more likely the movement, beginning as early as 1964, of men toward the Republican Party. During this same period, women generally stuck with the Dems.

The reason for the shift:

According to political scientists, the primary influence seems to be their different attitudes toward social-welfare spending … but the difference grew more noticeable when the role of “big government” and rising budget deficits became an increasingly important wedge issue. Reining in government growth was central to Reagan’s 1980 campaign, and the desire to limit taxes and spending has continued to be a salient theme among Republican candidates. Democrats, meanwhile, have consistently sought to portray themselves as protectors of the social safety net.

That said, the GOP appears to have the losing side of the gender gap given that the proportion of women voting tends to be higher than that of men, DiA notes. An earlier look at the gender voting gap here.