The Supreme Court of the United States (SCOTUS) is set to hear two historic arguments that will decide the legality of same-sex marriage in the US.

Today the Court will hear a one-hour oral argument on Proposition 8, the California constitutional amendment which in 2008 ruled that only heterosexual marriages were recognised in the state.

There is a wide spectrum of possible rulings the Court could make: it may decide to uphold Proposition 8, allowing the state ban and others like it to stand; it may make a narrow ruling that only the California ban should be struck down, leaving other states to make their own decisions; or it may decide to rule all state bans on same-sex marriage unlawful.

On Wednesday there will be oral arguments on the Defense of Marriage Act, which was signed into law by President Bill Clinton in 1996. The law nationally defines marriage as “a legal union between one man and one woman”.

Mr Clinton has recently said “I have come to believe that DOMA is contrary to [constitutional] principles”, and his wife, former US Secretary of State Hilary Clinton, came out in support of marriage equality in a video last week.

Recently, evidence has emerged that the tide of opinion among the public and lawmakers is turning in favour of marriage equality.

Democratic Senator Claire McCaskill and Republican Senator Rob Portman are the most recent politicians to officially announce their support for same-sex marriage.

A widely cited poll published one week ago revealed 58% of Americans now support the legalisation of same-sex marriage, while 36% oppose it.

Despite the trend toward support for same-sex marriage, Daily Beast analyst Michael Tomasky predicted that SCOTUS may still uphold Proposition 8 as the conservative Justices may take a hard line to make a political point.

“They might see themselves, what with people like Senator Portman buckling to the sodomite lobby, as the last line of defense, the last moral men in a crumbling universe,” he said.

David Boies, one of the country’s top attorneys who will be arguing for Proposition 8 to be overturned, predicted the Justices would rule overwhelmingly in favour of marriage equality, saying “It’s going to be 7-2″.

A decision on the cases is likely to be made by the end of SCOTUS’s term in June.