The Democratic Party of the United States supports marriage rights for gay and lesbian couples, included in its official party platform in 2012. About two-thirds of self-described Democrats supported same-sex marriage in 2012, a percentage that has risen sharply since 2008, when only half of Democrats were in favor of extending marriage rights to gay couples, reports the Pew Research Service. Although support for marriage equality has also reached record levels among the American population as a whole, it remains a polarizing political subject. The Republican Party, in its official 2012 platform, defined marriage strictly as a institution between a man and a woman. In 2012, Democrat Barack Obama became the first sitting U.S. president to publicly support same-sex marriage rights.

Support From Democrats Is Recent

The 2012 Democratic National Platform was the first in U.S. history to support same-sex marriage rights. That policy shift was included after President Barack Obama affirmed his support for marriage equality in May 2012, making the Democrats the first major political party to embrace that position. Although the platform drafted in 2008 called for “equal responsibility, benefits and protections” for same-sex couples and their families, it stopped short of endorsing marriage rights due to the fact that Obama -- the Democratic presidential candidate – did not publicly support it at the time.

Legal Same-Sex Marriage Starts in Blue States

The heavily-Democratic Massachusetts became the first state to legalize same-sex marriage in 2003. While a majority of the 17 states that recognize gay marriage, at the time of publication, are Democratic strongholds, political swing states like New Hampshire and Iowa also recognize those unions. In 2012 Maine, Maryland and Washington – all states that vote largely Democratic – became the first states to legalize same-sex marriage through popular vote.

Gay Marriage Supporters

Less than a quarter of self-described Republicans were in favor of gay marriage in 2012, according to the Pew Research Center compared to 65 percent of Democrats. Among liberal Democrats, that support rose to an overwhelming 83 percent in July 2012. Americans below the age of 35, at 63 percent, were, similarly, considerably more likely to support gay marriage compared to older generations. Although adults above the age of 67 were the least likely to approve of it, support among that demographic jumped almost 10 percentage points, from 24 percent to 33 percent, between 2008 and 2012.

Support For Alternative Forms of Marriage

Many conservative Republicans have claimed legalizing marriage rights for gay couples would be a “slippery slope” that could eventually lead to the legalization of crimes such as polygamy and bestiality. However, there is no evidence to suggest those claims are within the realm of possibility. Just 14 percent of Americans described polygamy as “morally acceptable” in 2013, according to a Gallup poll. The Democratic Party platform exclusively endorses marriage rights for homosexual and heterosexual adult couples.