The Supreme Court declared same-sex marriage bans unconstitutional today, and I think Karl Rove and George W. Bush deserve a golf clap today. Gay rights were only beginning to blossom as a national political issue, and same-sex marriage even further off the radar, when Rove decided that using same-sex referenda as a wedge issue to force Democratic stumbles and boost evangelical turnout in 11 key states, including Ohio, which W. won narrowly (CNN refused to call the state until the wee hours) and whose electoral votes were decisive.
But that had the unintended effect of massively shifting the Overton Window and dragging what might have been a political fight as far away as the 2020s into the 2000's-2010's. You can see from this helpful XKCD that 2004 was an inflection point for gay marriage, after which the rate of approval, which had climbed slowly to about one-in-three and then plateaued, skyrocketed to majority national approval within five years.
The referenda changed the discussion from "do we accept gays as full members of society" to "should gays get married" which almost presumed the previous question. This seems hard to remember, but in 2004 the question of "is being gay OK" was one that was still not settled completely in this country. I mean, without appealing to memories of what that time was like (homophobia was everywhere) holy crap look at this polling data:
So though in 2004 enough Americans still thought gays were gross and gay marriage was weird to help push a narrow electoral victory, it ended up being a fatal blow in the medium term to the social conservative agenda.