Almost two out of three Democrats (65 percent) now support same-sex marriage, according to a Pew Research Center poll – a 15 percentage point increase since 2008.
In 2008, Democrats were evenly split, with 50 percent supporting gay marriage. In 2004, only 40 percent said they supported gay marriage. Self-described liberal Democrats were the most supportive of gay marriage, at 83 percent. Conservative and moderate Democrats were more closely divided with 54 percent supporting gay marriage.
Pew's poll was released a day after reports surfaced that the Democratic Party platform will likely include support for gay marriage for the first time.
The poll shows increasing support for gay marriage among all Americans, who are now about evenly split on the issue. Forty-eight percent of the full sample support gay marriage, a nine percentage point increase from 2008 (39 percent) and a 17 percentage point increase from 2004 (31 percent).
Republicans are the most opposed to gay marriage. Only 24 percent support gay marriage, a five percentage point increase since 2008, when it was at 19 percent. Independents fall between the partisans. Fifty-one percent support gay marriage, a seven percentage point increase since 2008, when it was at 44 percent.
President Barack Obama was opposed to gay marriage when he was a candidate for the U.S. Senate in 2006 and a presidential candidate in 2008. On May 9, 2012, he announced that he changed his mind and now favors same-sex marriage.
Pew's polling suggests that Obama's announcement did little to change public opinion. Two polls conducted after the announcement show nearly the same support for gay marriage as a poll conducted in April.
There are also differences in support based upon religious membership and participation. Those most opposed to gay marriage include white evangelicals (73 percent) and those who attend religious services weekly or more (65 percent). Those most supportive of gay marriage are atheists and agnostics (88 percent), those who say they have no religious views in particular (65 percent) and those who seldom or never attend religious services (66 percent).
The June 28 to July 9 poll of 2,973 Americans has a plus or minus 2.1 percentage point margin of error for the full sample. The margin of error is 3.6 percentage points for Democrats, 4.1 percentage points for Republicans and 3.5 percentage points for independents.