Prominent liberals are pleading with third-party candidate Ralph Nader (searchto abandon his "quixotic and destructive" presidential bid, warning that his presence in the race could ensure the re-election of President Bush.

Fifteen progressive and liberal organizations, including Americans for Democratic Action (search) and Council for a Livable World (search), sent a letter to Nader Thursday praising his work as consumer advocate but arguing that he cost Democrat Al Gore the 2000 election.

Nader's percentage of support in Florida and New Hampshire, if it had gone to Gore, would have secured those states and the presidency for the Democrat.

"You have done great things in your career as a consumer advocate and we applaud your work, but your presidential race in 2000 led to the most destructive administration we can remember in our 200-plus collective years of progressive advocacy," the groups wrote.

Nader ran as the Green Party (search) candidate in 2000 and is seeking the presidency this year as an independent, to the dismay of many Democrats who have appealed to him not to run.

"We call on you to stop this quixotic and destructive effort," the groups wrote. "The stakes are simply too high. We cannot afford another four years of George W. Bush, but your candidacy only serves to help his re-election campaign."

Nader consistently has rejected these pleas and has disputed the suggestion that he cost Gore the election.

Speaking to about 400 students and supporters at Shenandoah University in Virginia Friday, Nader did offer a bit of a concession, saying, "Al Gore slipped on about 18 banana peels and maybe the Green Party was one of them."

The Nader campaign turned down the latest plea from the groups.

"You have to stand for something and I think these liberal groups, with their anybody-but-Bush advocacy, are going to get nothing in return," said Nader spokesman Kevin Zeese.

Although not on any states' presidential ballot, Zeese said the campaign was moving ahead, raising nearly $475,000 in the first two months of this year with $260,000 on hand entering March.

At Shenandoah University, Nader said he wants to work with presumptive Democratic nominee John Kerry on common issues.

Current polls show Nader getting enough support to alter the Bush-Kerry race. Nader generally registers about 5 percent, with many of his supporters independents and young voters.