It takes a particularly noble Democrat to promote marriage and family. The strengthening of these institutions is not in the Democratic Party's self-interest. The more people marry, and especially the more they have children after they marry, the more likely they are to hold conservative values and vote Republican.
That is why it is inaccurate to speak of a "gender gap" in Americans' voting. The gap is between married and unmarried women. Single women, especially single women with children, tend to vote Democratic, while married women, especially married women with children, tend to vote Republican.
Why is this?
There are two primary reasons.
One is that women's nature yearns for male protection. This is a heretical idea among the well educated whose education is largely devoted to denying the facts of life. But it is a fact of life that can easily be proven: Extremely wealthy women almost always seek to marry men who are even wealthier than they are. Actress Jane Fonda had more money than almost anyone in America, yet she married Ted Turner, a man who had even more money than she. Though fabulously wealthy and a feminist, Ms. Fonda nevertheless could not shed her female nature.
Given women's primal desire to be protected, if a woman has no man to provide it, she will seek security elsewhere -- and elsewhere today can only mean the government. In effect, the state becomes her husband. This phenomenon has frequently been commented on with regard to the breakdown of many black families. The welfare state simply rendered many black men unnecessary and therefore undesirable as spouses: Why marry when you can get more benefits from the state while remaining single (and get even more money if you have children while remaining single)?
Once a woman does marry, however, her need for the state not only diminishes, she now begins to view the state as inimical to her interests. For the married woman, especially if she has children, two primal urges work against her having a pro-big government attitude. Her urge to be protected, which is now fulfilled by her husband, and her primal urge to protect her nest are now endangered by the government, which as it grows, takes away more and more of her family's money.
Once a woman marries and has children, therefore, her deepest desires -- to be protected and to protect her family -- work as strongly on behalf of conservative values and voting Republican as they did on behalf of liberalism and the Democratic Party when she was single.
The other reason married women are less likely to be liberal and vote Democratic relates to maturity and wisdom.