Nate Silver posted this on his blog:

Source:  Nate Silver’s Blog

The date, he says: “According to surveys included in the PollingReport.com database, an average of 50 percent of American adults support same-sex marriage rights while 45 percent oppose it, based on an average of nine surveys conducted in the past year.”

President Obama came out in support of same-sex marriage. However, Nate Silver notes:

“It should be remembered that support for same-sex marriage in polls has not necessarily translated into support at the ballot booth. On Tuesday, North Carolina became the latest state to adopt a Constitutional ban on same-sex marriage and did so by a margin of about 20 percentage points, somewhat larger than polls forecast. The North Carolina measure also banned domestic partnerships and other types of civil unions.”