Late last week, GOP Sen. Rob Portman shocked commentators and fellow politicians by reversing his position on same-sex marriage, saying that his decision was inspired by his son, who is gay. In my latest for “Figuring Faith,” I show that this “family and friends effect” is quite potent when it comes to the issue of same-sex marriage:

Even on controversial issues such as same-sex marriage, public opinion research demonstrates that relationships with family and friends often trump political and religious affiliations.

Since 2011, polls have consistently shown pluralities or slim majorities of Americans—including many religious Americans such as Sen. Portman’s fellow mainline Protestants—have come to support allowing gay and lesbian people to marry legally. It is also well known that the polls also show as much as a forty-point generation gap between the youngest and oldest American adults on this issue.

But what is less known is what might be called the “friends and family effect”: the nearly 30-point gap that exists in attitudes on same-sex marriage between those who have a close friend or family member who is gay or lesbian, and those who do not. Among the approximately 58 percent of Americans who report having a close friend or family member who is gay or lesbian, six-in-10 (60 percent) support allowing gay or lesbian couples to marry, compared to 35 percent who oppose it. Among Americans who do not have a close friend who is gay or lesbian, opinions are a mirror image: only three-in-10 (31 percent) support same-sex marriage, and 62 percent oppose it.

To read the full column, head to “Figuring Faith,” my Washington Post blog.