Demonstrators from both sides of the argument gathered outside the US Supreme Court as it prepared to hear whether same-sex marriage should be a constitutional right nationwide.<br /><br /> Nine judges are due to determine the issue by the end of June.<br /><br /> With four liberal judges expected to back gay marriage, all eyes are on one conservative who could cast the decisive vote.<br /><br /> In the past Justice Anthony Kennedy has broadened the court’s view of sexual equality.<br /><br /> Same-sex marriage is currently recognised in a 37 American states and Washington DC.<br /><br /> The legal arguments centre on four of 13 states that currently ban it: Kentucky, Michigan, Ohio and Tennessee.<br /><br /> Public support for gay marriage has steadily grown in recent years. It’s particularly strong among younger Americans. Barack Obama is the first sitting president to support it.<br /><br /> The Supreme Court must decide whether legal guarantees of due process and equal protection oblige states to allow same-sex marriage – and whether they must recogn
