Unmarried Voters Have the Numbers, If Not the Attention

Michael Cuellar isn’t moved when presidential candidates talk about aiding middle-class families and offering child-care tax breaks. Such perks wouldn’t help the 27-year-old Austin, Texas, startup worker, who plans to remain a childless bachelor for years.

He is part of what sociologists see as a growing disconnect between the messaging of political campaigns and a dramatically changing U.S. electorate. Nearly half of adults in America are unmarried, while the rate is even higher among those under age 35, now the largest...