Same-sex marriage, promised in Britain before the next general election, was conspicuous by its absence from the Queen's Speech on Wednesday. But on the same day on the other side of the Atlantic, Barack Obama became the first US president to express his support for the idea. In doing so, he placed himself on the right side of America's most contentious social issue, and on the right side of history. It can only be hoped that David Cameron will prove equally courageous in the face of the increasingly vocal opposition to the proposal from the Tory right.

In the US, gay rights advocates will complain that the President should have expressed himself earlier and more forcefully, rather than seeming to have his hand forced by the unexpected endorsement for gay marriage by Vice-President Joe Biden on a Sunday talk show. They will also object that Mr Obama stressed that his was a personal view, and that the matter should be decided by individual states.

But Mr Obama's caution was understandable. Already, no president had been more supportive of gay issues. But until Mr Biden spoke out and triggered a media frenzy, the White House had maintained merely that the President's position on same-sex marriage was "evolving". Nor, although it carries great symbolic importance, will Mr Obama's voice be decisive. As with momentous earlier battles over equal rights and the "separate but equal" principle that underpinned racial segregation, the legality of same-sex marriage will almost certainly be resolved by the Supreme Court.

For the moment, re-election is Mr Obama's most pressing concern, and the political impact of his words is hard to predict. His stand may cut into his support from blacks and Latinos, and will undoubtedly energise the Republican base. But the economy remains key, and the election will not hinge on the issue of gay marriage.

Meanwhile, time will probably render the issue moot both in the US and closer to home. Younger voters increasingly regard gay marriage as natural and acceptable, and, in a few decades, all will wonder what the fuss was about. Not a moment too soon.