The US Senate has blocked a constitutional amendment banning same-sex marriage.
President George W Bush had backed the ban, saying marriage between a man and a woman was the most fundamental institution of civilisation.
But the motion gained the votes of 49 senators, 11 short of the 60 needed to allow the process to go forward.
Critics say Mr Bush is trying to win back disillusioned Republican voters ahead of November’s mid-term poll.
Supporters of the amendment remained defiant.
“I do not believe the sponsors are going to fall back and cry about it,” Republican Senator Orrin Hatch said. “I think they are going to keep bringing it up.”
An amendment to the constitution is necessary because activist courts have left our nation with no other choice
President Bush
Matt Frei diary: Bush rhetoric
But Democrat Senator Edward Kennedy called it a “cynical attempt to score political points by overriding state courts and intruding into individuals’ private lives”.
The decision to throw out the ban was not a surprise and broadly reflects a national consensus, the BBC’s James Coomarasamy in Washington says.
Although a majority of Americans oppose same sex marriage, most want individual states to make their own decisions about the issue, our correspondent adds.
Energising issue
The subject of gay marriages has been much debated in the US since Massachusetts became the first state to issue marriage licences for gay couples in 2004.
Forty-five of 50 states have passed laws or amended their constitutions to effectively prohibit same-sex marriages.
But several of those bans have recently been rejected by judges in states, including Washington, California and New York.
Mr Bush said: “Ages of experience have taught us that the commitment of a husband and a wife to love and to serve one another promotes the welfare of children and the stability of society.”
“An amendment to the constitution is necessary because activist courts have left our nation with no other choice.”
Although a similar ban was defeated in 2004, it proved an issue that energised socially-conservative Republicans in that year’s presidential poll, our correspondent says.
A constitutional amendment needs two-thirds support in both the House and the Senate.