We all know the famous Norman Rockwell painting of a typical American family gathered around Grandma as she serves up a huge turkey. If Rockwell were painting today, his portrait of a Thanksgiving feast would have to include gay Uncle Kevin and perhaps a niece who’s brought her girlfriend home from college. (He might also sketch in the new Chinese daughter-in-law, but that’s another story.)

The American family is changing rapidly, and so are attitudes about same-sex marriage. In the last election, three states voted to approve the institution (Maryland, Maine and Washington), and one, Minnesota, rejected a move to ban it. The focus on Barack Obama’s re-election, and the attention paid to the critical Latino vote, obscured this historic milestone.

For the first time, after more than 30 failed tries, gay marriage was approved by statewide vote. (Until now, it took court decisions or legislative action to enact the laws.) That means same-sex unions are now legal in nine states and the District of Columbia, and advocates are planning a half-dozen more campaigns in the next few years.

In the latest ABC News/Washington Post poll, 51 percent supported marriage equality, up sharply from 32 percent just eight years ago. And the trend line is clear. Among young adults, more than six in 10 favor the right of same-sex couples to wed legally.