With six recent polls showing support for same-sex marriage at 59 percent, 56 percent, 55 percent, 55 percent, 54 percent, and 53 percent, it seems like a good time to make another graph of the polling data. The following figure shows the net support for marriage equality in 175 polls over the past 29 years—the percent in favor minus the percent against. I've labeled a handful of notable events for orientation. The line is a Loess regression model.
But first, this line will likely keep going up in the long term. Why? One, conservatives have spent millions and thrown everything they had against marriage equality; the result has been only temporary drops in support at worst. Two, and this cannot be repeated enough, because young people are far more supportive of marriage equality than the oldest cohort they are replacing. Support in the general population will continue to rise as long as this remains true (and I've seen no evidence to suggest it will change).
For those who like getting lost in the details, in the graph below, I have added a panel showing the rate of change of the regression line (this should be interpreted with caution), and a panel showing victories and defeats when same-sex marriages either were recognized as legal, or banned (DOMA is included).
Polling on the opinions of same-sex marriage, or marriage for homosexual couples (the wording used in some early polls), was not common prior to the fight over DOMA. What data we do have show net support rising quickly as the idea of same-sex marriage first entered public debate.
The process of passing DOMA likely resulting in a setback for public support; at the very least, public opinion stalled for several years. By 2000, however, net support was clearly growing again.
Then came Lawrence v. Texas.
The Great Panic of '03
Lawrence v. Texas was handed down by the Supreme Court on June 26, 2003. The very next day, Gallup went in the field with a poll; Pew had actually already started a poll on June 24th. These polls found what was then a record high net support of -15 for same-sex marriage, and the second highest recorded net support (-16).
By October, however, net support in the Pew and Gallup polls had plummeted to -27 and -26. This was prior to the decision legalizing same-sex marriage in Massachusetts on November 18, 2003.
Between these two sets of polls, I vaguely recall a right-wing freakout, and apparently it was a successful one. On August 10th in the New York Times, Elisabeth Bumiller explained to us "Why America Has Gay Marriage Jitters:"
What happened? Pollsters, sociologists and gay rights leaders say the answer lies in large part in the culturally explosive word "marriage," which entered the debate after the Supreme Court ruling in June. The word came first from Justice Antonin Scalia, who in a sharp dissent to the sodomy decision accused the court of having "largely signed on to the so-called homosexual agenda." He predicted that same-sex marriage would be the logical next step.In other words, same-sex marriage suddenly became The End of the World As We Know It. The Right-Wing Noise Machine went into high gear, and support for marriage equality fell dramatically.
Social conservatives quickly took up the warning that traditional marriage as Americans knew it was gravely endangered. President Bush was pressured by his conservative supporters to oppose gay marriage publicly, which he did last month in the Rose Garden — when he used a question about homosexuality to talk specifically about gay marriage.
Standing Athwart History, and Getting Run Over
By the end of 2004, support for marriage equality had fallen to where it had been approximately ten years previously. The forces of bigotry had a dozen wins racked up for the year. Some analysts were even crediting them with the re-election of Bush via increased conservative turnout for anti-marriage ballot measures.
Ever since then, however, support for marriage equality has only grown, although the growth seems to have slowed down for the election years of 2008 and 2012. Currently, the rate of change is at record highs at about 10 points of net support per year (at least until the next Fox poll chimes in—Fox polls have, shockingly, almost always shown the lowest numbers of all).
Interestingly, two recent major events appear to have had little effect on public opinion. Obama's interview supporting marriage equality and the Supreme Court's ruling on the constitutionality of DOMA don't seem to have interrupted the trends in progress at the time. This doesn't mean, however, that they had no effect on public opinion. For instance, perhaps without the DOMA ruling, public opinion would have stalled out last summer. Also, they could have had temporary effects that aren't apparent on this graph. PPP state polls did show, collectively, larger increases in support for same-sex marriage in the month following Obama's announcement; the trendline in the graph above shows this was a short-lived phenomenon, however.
Today, support for marriage equality is very strong in the United States, even among young Republicans. The string of defeats has petered out while the rapid-fire successes are beginning to seem almost commonplace, as state after state begins to issue marriage licenses to same-sex couples.
The two most comprehensive data sources are PollingReport.com and the American Enterprise Institute(!). For one poll, the oldest (1985), I can find no information other than a brief discussion of the results in a 2008 post by Charles Franklin. Please note that wording varies from one poll to another. Wins and losses are marked as of the day a bill is signed, a ballot measure is passed, or a court decision is handed down (even if it is stayed).