US President Barack Obama has become the first sitting president to back gay marriage.
Yesterday, he ended months of hedging on the issue of gay marriage by saying he thinks same-sex couples should be able to wed.
Mitt Romney, the Republican who is set to challenge Obama for the White House in November's elections, promptly said he was against gay marriage.
In recent days, Vice-President Joe Biden and cabinet member Arne Duncan had expressed support for gay unions.
A Gallup poll on Tuesday suggested that 50 per cent of Americans were in favour of legalising gay marriage, while 48 per cent said they would oppose such a move.