Same-sex marriage is now legal in nine states and the District of Columbia. Civil unions are legal in eight more states, with Colorado on the verge of joining. Many other states have outlawed gay marriage.
Americans' attitudes, especially among Democrats, have tipped the balance on gay marriage in the space of one presidency. Obama, Clinton, Biden and other Democratic presidential candidates opposed legalizing same-sex marriage in 2008, although they endorsed versions of civil unions.
Clinton's bigger problem that year involved a different issue: opposition to the Iraq war, which had become deeply unpopular with Democratic voters by 2007. Clinton defended her 2002 Senate vote authorizing an invasion of Iraq. Obama, as an Illinois state legislator, had condemned the war from the start. By lagging behind Obama on this key issue as the 2008 primaries approached, Clinton lost valuable ground to the lesser-known lawmaker from Illinois.
With major Democratic politicians now taking a similar stand on gay marriage, the issue seems unlikely to play the type of role in 2016 that the Iraq war played in 2008.
President Bill Clinton signed the Defense of Marriage Act in 1996. DOMA requires the federal government to refuse to recognize same-sex marriages. It also allows states to do the same when dealing with gay or lesbian couples married in other states.
In 2000, Hillary Clinton was typical of prominent Democrats in saying marriage "has a historic, religious and moral context that goes back to the beginning of time. And I think a marriage has always been between a man and a woman."
Bill Clinton recently wrote an op-ed saying it's time to overturn DOMA. The Supreme Court will hear a challenge to the law this month.
As support for gay marriage becomes the mainstream position among Democrats, the issue is increasingly divisive among Republicans. Sen. Rob Portman of Ohio last week became the only Republican senator to support legalizing same-sex marriage. He did so after learning that one of his adult sons is gay.
Dozens of prominent Republicans have urged the Supreme Court to overturn DOMA. But many GOP-controlled states have asked the court to uphold the law.
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