There's so much research done regarding how people make voting decisions. People generally vote with how they feel about a candidate, so as long as marriage remains a status quo in american culture and it increases a persons relatability, then i doubt you'll see a non married person for the head office. Paradigms certainly shift, and there's lot of examples of non-married elected officials, however the national narrative dictated to us seems to put a lot of stock in people being married. Just look at the earlier republican candidate debate, and how much they spent talking about their families.
http://www.thedailyshow.com/...lican-debate-is-a-success
Totally irrelevant (at least in my mind) to a persons ability to govern, but gee someone must think it is, because it comes up a ton.