In an announcement that electrified activists around the globe, President Obama came out yesterday in favour of gay marriage. This is the first time that a sitting US president has backed marriage equality. In an election year, the significance is all the greater.

Some think it's a risky move. Fifty percent of Americans believe same-sex marriages should enjoy the same rights as traditional marriages, while just under half say they should not even be legal.

But after years of sitting on the fence, claiming his position was "evolving", the president has finally made his position unequivocal: “It is important for me to go ahead and affirm that I think same sex couples should be able to get married," he said yesterday.

One nation, hotly divided

Support for same-sex marriage has grown steadily in the United States in recent years, but people remain sharply divided on political and religious grounds. A recent Gallup poll found that two-thirds of Democrats support legalising gay marriage, while just 22% of Republicans favour it.

In the 24 hours before Obama’s announcement, Republican leaders in Colorado killed a law that would have allowed civil unions, and North Carolina voters passed a ban on gay marriage – the last time the state had altered marriage law was to ban interracial marriage back in 1875.

But the fact that the ban passed by more than a 20-point margin in North Carolina, a key battleground state, raises questions about what Obama’s move could mean for him in the November election. Six "swing states" have already passed gay marriage bans and same-sex marriage does not poll well among two key voting blocs for Obama: African Americans and Latinos.

Yet the move will certainly have injected energy into Obama’s supporter base and is likely to be a boon for fundraising. As columnist Carter Eskew pointed out, “[i]t restores the view of him as a principled, idealistic leader who is not afraid to do what is right... Yes, the president has given more fodder to his opponents, but their stockpiles runneth over already.”

Let the mudslinging begin

Republican rival Mitt Romney underlined his own opposition to same-sex marriage just hours before the announcement, expressing support for an amendment to the US Constitution that would ban it outright, for all states. And former presidential hopeful Rick Santorum responded to Obama's announcement by claiming the president had failed to protect "the institution of marriage from radical social engineering at both the state and federal level".

Despite growing support for marriage equality, every time the issue has been taken to the polls, citizens have voted against same-sex unions.

While Obama’s historic move may mark a turning point in this struggle, the devastating impact of current policies are poignantly clear in this video, released by Shane Bitney Crone on the first anniversary of his partner’s tragic death: