Despite a huge collapse in support compared to 2000 and little organisation on the ground, Mr Nader's meagre showing could still prove a decisive factor in a tight race.

"The reality is the Nader factor is arguably still there," Chris Kofinis, senior adviser to the anti-Nader group TheNaderFactor.com told the Associated Press. "But we've been incredibly successful at minimising it in part because of Nader's own failings and in part because people don't buy his message anymore."

Democrats accuse Mr Nader, an anti-corporate crusader, of handing the election to George Bush in 2000 by siphoning votes that would have gone to Al Gore. Mr Nader, who gained 2.7% of the vote nationwide, won more than the margin between Mr Gore and Mr Bush in New Hampshire and Florida.

Exit polls from 2000 show that two thirds of those who voted for Mr Nader would not have voted otherwise and Mr Nader replies that he took more votes from Republicans in New Hampshire and Mr Gore was defeated because he could not win his own state, Tennessee.

But many prominent left wingers who backed Mr Nader in 2000, including Noam Chomsky and Michael Moore, have abandoned him this year, arguing that his candidacy will be counterproductive.

Democrats have successfully sought to keep Mr Nader off the ballot around the country by challenging the signatures he has submitted. Mr Nader has condemned "dirty tricks, harassment and intimidation" by Democrats.

"If you're not willing to lose in politics, and fight and lose again, and fight and lose again, your agenda will never prevail," he said last week.

He will still be running in many battleground states, including Florida, Minnesota, Iowa and New Hampshire where the race between Mr Bush and Mr Kerry is effectively tied.

But in many of the areas where he performed best last time, such as Minnesota and Colorado where he attracted 5% of the vote, his support has effectively collapsed, bumping along between 1% and the asterisk of an also ran.

Polls vary on whom Mr Nader hurts most. A recent Gallup poll suggested 52% of those backing him would otherwise vote Republican, as opposed to 48% who would go to the Democrats. Others have shown his voters favouring Mr Kerry to Mr Bush by three to one.