According to Mark Whiteis-Helm, the spokesman for the political wing of Friends of the Earth (FoE), the decision reflects both disillusionment with Mr Gore's environmental performance over the past seven years and recognition of Mr Bradley's superior credentials. He said that the group had made the decision only after much deliberation and, "to an extent, with heavy heart, as Mr Gore was one of the first people in the White House to address environmental concerns". However, detailed comparisons of the two candidates' records when they were senators had shown that Mr Gore's record was "not good at all".
In a statement, FoE said that Mr Bradley had a far higher rating than Mr Gore from the League of Conservation Voters - 85 per cent compared with Mr Gore's 66 per cent. But it also reproached Mr Gore for being "part of an administration which has done significant international environmental damage". Specifically, it accused him of accepting legislation that had weakened protection of the ozone layer and of opposing the stronger measures favoured by the Europeans.
This criticism leaves Mr Gore, who has traded on his "green" reputation ever since publishing his book Earth in the Balance, in the worst of all worlds. In the US, he is more often criticised for "selling out" national interests at the Kyoto summit in Japan in 1997 by accepting emissions curbs greater than US industry would have liked, and the treaty has still not been submitted to the US Senate for ratification.
Mr Gore's camp put a brave face on the announcement. His press secretary, Kiki Moore, declined to comment, maintaining only: "Al Gore has long believed in and worked for a balanced approach to making a clean and healthy environment a reality for America's working families."
Eric Hauser, spokesman for Mr Bradley, said: "We're very happy to get this support because it reflects Bill Bradley's ability to get big things accomplished." Some of the early criticism of Mr Bradley questioned whether he was too theoretical and idealistic to forge the alliances necessary to get legislation through.
The FoE endorsement is just the latest setback for Mr Gore's accident- prone campaign, and came on a day that saw the release of another opinion poll - the fourth in 10 days - showing Mr Bradley gaining strongly on Mr Gore in the key primary state of New Hampshire. This poll, conducted by the University of New Hampshire, for CNN and a local radio station, showed Mr Gore supported by 46 per cent of likely voters in next February's primary, with 41 per cent for Mr Bradley - double the support he registered in May.
While FoE is relatively small compared with other environmental organisations in the US, it has political clout that extends far beyond its 20,000 paid-up members. It has forged strong links with congressional groups and allied itself with other political lobbies, such as Taxpayers for Common Sense, so as not to isolate itself from the mainstream.
There is also a difference in the priorities of the groups and the age- range of voters with whom their opinions will count. The more established groups are known for their work in conserving endangered creatures (the bald-headed eagle and the spotted owl) and habitats, and the Sierra Club has a sideline interest in population control. FoE has taken on issues such as genetically modified crops, which are causing increasing concern in the US, especially among the middle classes and younger people, and are arguably the issues of the future.