But at the same time support has grown, The Fix’s Rachel Weiner points out that efforts to legalize gay marriage have fared pretty horribly at the ballot box:

Thirty-two times since 1998, voters have gone to the polls and voted against gay marriage. Thirty-eight states prohibit gay marriage in some fashion. Even in “blue” states like California, Oregon and Delaware, gay marriage bans stand. North Carolina’s Amendment One Tuesday night was just the latest in a long line of failures at the ballot box for proponents of gay marriage. (Support for bans is falling over time, according to HRC: in 2004 they passed on average 71 percent to 29 percent, but in 2008 the average was 57 percent to 43 percent.)

The six states with legal gay marriage have all gotten there through the courts or the legislature; none have done so by popular vote. So how does gay marriage keep losing the popular vote at the same time that it’s becoming more popular?

Some of it, Weiner notes, comes down to timing--especially in North Carolina, which passed an amendment barring same-sex marriage on Tuesday. “North Carolina was the last state in the South to pass a constitutional amendment banning gay marriage,” she notes. “It likely would have come up earlier if Democrats had not held the state’s legislature for 140 years straight.”

Location matters, too: Ballot initiatives to ban gay marriage have tended to come up in more conservative states, places like Georgia, Mississippi, Kentucky and Louisiana.

But some of it might have nothing to do with gay marriage at all, and everything to do with the vehicle: The ballot initiative. The majority of issues put to a public vote tend to fail - and that’s been true since the early 1900s, according to analysis from the Initiatives and Referendum Institute. A total of 2,314 state-level ballot initiatives have gone to public vote since Oregon offered the first in 1904. Of those, fewer than half - 942, or 41 percent - have been approved.

“One rule of thumb widely known among initiative consultants is that ballot initiative issues are generally easier to kill than pass,” Ron Facheux, editor in chief of Campaigns and Elections, wrote in a 2001 article on the issue. “To pass a proposition, you have to offer a compelling reason why the change is both needed and desired. To defeat one, usually all you need to do is raise doubt.”