prior to 1980 8% gender gap, there were five prez elections in which one candidate apparently recieved appreciably higher percentage (above statistically insignificant 2-3%) of votes from women than men - 4% for Republican Hoover in 1928 (based on straw polling, not so-called scientific polling) thought to be result of more women supporting Prohibition, 6% for Hoover in 1932 (based on 1936 survey asking prospective voters who said they had voted in previous election), 5% for Republican Eisenhower in 1952 (based on exit polling) thought to be result of more women blaming Democrats for Korean War, 6% for Eisenhower in 1956, 5% for Democrat Carter in 1976 who campaigned actively in favor of ERA...
so gender gap favoring Dems since 1980 correlates with re-emergence of women's movement in 1960s/1970s and with different attitudes by national parties towards women and women's rights in last two decades...in 1980, Reps became first major party since 1940 not to endorse ERA and in 1981 Reagan became first prez not to support the amendment since Truman... Michael Hoover