Women make up 50.8% of the United States population. But when it comes to electoral politics, women make a much bigger difference. They simply vote in a higher percentage and in higher numbers than men do. For instance, in the 2012 presidential election, 71.4 million women voted (63.7% of eligible women) and 61.6 million men voted (59.8% of eligible men). That means women made up 53.7% of all voters in 2012. And this higher number and percentage of women voters has been true in every election since 1980.
There is no reason to believe the 2016 election will be any different. That makes the women's vote a very important consideration for any candidate wishing to make a serious run for the presidency. And at least for now, Hillary Clinton is much more popular among women than any other candidate (of either party). She has a 56% favorable rating among all women to only a 32% unfavorable rating -- and that favorable over unfavorable rating extends through the differing groups of women.
In addition, her favorability among women is significantly larger than the favorable rating of any other candidate. This gives her a clear head start over any other candidate -- especially since men are split (44% to 45%) on Hillary Clinton (which means another candidate couldn't count on men to offset the clear advantage Clinton has among women).
These numbers are from a recent Gallup Poll -- done between March 2nd and 4th of 770 women (and 752 men), with the margin of error for each group being 4 points.
