The US president became the first American leader to voice public support for same-sex marriage, during an interview with ABC News on Wednesday.
His endorsement comes six months before he will likely face Republican challenger Mitt Romney, who opposes gay marriage, as does roughly 48 per cent of the population. More states have outlawed gay marriage than have voted to recognise it.
But Obama's watershed moment was a calculated one: He said that despite his personal convictions, he still believes states should decide the issue. That is essentially the same stance taken by former Republican Vice President Dick Cheney.
Al Jazeera's Patty Culhane reports from Washington D.C.