On the other hand, nonmarried voters break strongly for the president over Romney, 56% to 35%. Marriage is a significant predictor of presidential vote choice even after income, age, race, gender, education, religiosity, region, and having minor children are statistically controlled for.
September 14, 2012
"Married registered voters prefer Republican challenger Mitt Romney over Democratic President Barack Obama by 54% to 39%..."
Says Gallup (looking at June-August data):