Married men: for Romney by 54-35, Romney's margin 19.
Married women: for Romney, 49-42, Romney's margin 7.
Single men: for Obama, 47-38, Obama's margin 9.
Single women: for Obama, 60-31, Obama's margin 29.
Of course, it helps to remove the effects of race and so forth, but the effect of marriage is still very much there. One way to sum up the demographics of the American party system is that the Republicans are the party of married white people, and the more different somebody is from that norm, the more likely they are to vote Democratic.
Or you could look at it on a continuum: the Republicans are the party of married white fathers and the Democrats are the party of single black mothers.
From the Man from Mars' naive perspective, the party of married white fathers really ought to be able to beat the party single black mothers. But, perhaps the former has such an obvious advantage that it gets hijacked by special interests more? Or, perhaps the cultural industry is so bored and disgruntled with the natural ruling party that it makes vast efforts to make people feel that voting for the party of black single mothers is cool.