IT IS no secret that support for Mitt Romney and Barack Obama breaks down differently among men and women. But while this “gender gap” is typically discussed in terms of Mr Romney’s stance on so-called "women’s issues", such as abortion rights and contraception coverage, the evidence indicates that it actually reflects partisan differences over the government's social-welfare programmes. Moreover, the source of the gender gap has less to do with women and more to do with men moving away from the Democratic Party. If the gender gap is defined as the difference between men and women’s support for a candidate, most polls currently show it to be about ten percentage points for Mr Romney, who does better with men. (John McCain, by comparison, faced a gap of about five points in 2008.) Women have been consistently more likely than men to give the president higher marks, and there is evidence that more women than men have swung into Mr Obama’s column in the last month, helping to fuel a recent bump in the president's poll numbers. It wasn't always this way. The earliest studies of voters detected gender-based differences in the presidential vote in 1948, 1952 and 1956. Women, however, initially favoured the Republican candidates; by about four to six points, more women than men supported Tom Dewey and Dwight Eisenhower. Thereafter, however, the gender-based difference in presidential voting began to reverse, with women slightly more likely to favour the Democrat beginning in 1964. The gap grew noticeably wider in 1980, when Ronald Reagan won the election with greater support, by eight points, among men than women. Since Reagan’s election the gender gap has endured, more or less, with women consistently more likely than men to support the Democratic candidate. To be sure, this does not mean the Democratic candidate has always won the women’s vote—in fact, the Republicans did better with women in every presidential election from 1980-1992. It has only been since 1996 that a majority of woman voters have backed the Democratic candidate. (Bill Clinton won a plurality of the women’s vote in 1992, but less than the combined share won by George Bush and Ross Perot.)

It is tempting to blame the re-emergence and persistence of the gender gap, particularly since 1996, on the parties’ differences on women’s issues, dating back to 1980 and Reagan’s opposition to abortion and the Equal Rights Amendment. In this view, women have abandoned a party that has turned rightward on issues important to them. However, 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.

So why did men leave the Democratic Party, while women did not? According to political scientists, the primary influence seems to be their different attitudes toward social-welfare spending. (See pages 95-105 of Morris Fiorina's book for a short summary of the evidence.) Since at least 1948 men have tended to be more conservative than women on social-welfare issues, 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.

This all matters because party ID is the most important determinant of an individual’s presidential vote. And if social-welfare spending is the critical issue, it is unlikely that all the recent talk of women's issues, most notably at the Democratic convention, has done much to sway the vote. On the other hand, we have two candidates with very different views of government spending. A difference accentuated by Mr Romney’s 47% gaffe, which struck at the core of the male-female divide. Such a statement is likely to remind women why they have stayed true to the Democratic Party all these years (and was perhaps too tactless to win over men).

Since 1980, the proportion of women voting in presidential elections has been greater than the proportion of men. If that holds true come November, and if the magnitude of the current gender gap persists, Mr Romney will be hard pressed to beat Mr Obama despite his advantage among men. In the coming weeks the Republican nominee may be best served trying to convince woman voters that the sluggish economy has disproportionately affected society’s most vulnerable members, and that Mr Obama is to blame.