The recent defeat of America's Climate Security Act in the US Senate is unsurprising, if nonetheless disappointing. But with a new president in White House come January, the superpower will soon have another opportunity to show leadership on climate change.

One might have reasonably expected that the bill, sponsored by Senators Boxer, Lieberman and Warner, would muster the 60 votes needed on 6 June to quash Republican obstruction and pass through the Senate. After all, a majority of states have now enacted their own climate action plans. And buoyed up by a sea of scientific evidence on the perils of escalating emissions — most recently in a long-awaited report from the US Climate Change Science Program — backing for legal limits on greenhouse gases, as proposed in the bill, is at all-time high.

The US has clearly reached a tipping point in its stance on global warming, but the greatest challenge is now maintaining the momentum. Even if the bill had made it through the Senate, many suspect it would have fallen foul of a threatened veto by President Bush. Though the US legislative engine has come to a standstill, it is not a lost cause. Proponents of the Climate Security Act say that the support generated will provide much-needed drive for introducing a national 'cap-and-trade' system next year.

On the home front, some see June's Senate debate as a dress rehearsal that politically could serve to sway voters on an issue of massive public concern in the lead-up to the presidential elections. Further afield, the debate within the US Senate on such bold legislation is itself seen as a sign that change is afoot (http://www.washingtonpost.com/wp-dyn/content/article/2008/05/28/AR2008052802915.html). Both presidential candidates — Republican Senator John McCain of Arizona and Democratic Senator Barack Obama of Illinois — support mandatory emissions reductions through cap and trade. So regardless of who wins the election, the Climate Security Act is likely to provide the framework for future federal legislation.

That isn't to say that US commitment on climate change is a done deal from January. As Joseph Romm at the Center for American Progress writes on page 85 of this issue, far more immediate action than pricing carbon is needed to get the nation on an emissions trajectory that will ensure a sustainable climate for the planet. This, argues Romm, will require a prohibition on new coal-fired power plants plus the rapid deployment of existing clean technologies on a scale akin to the Apollo programme.

Both Presidential candidates have been playing cap and trade as their trump card in the climate policy game, but it's clear that whoever gains the White House in November will need to come up with an impressive hand to win against climate change both at home and beyond.