What all the groups have in common is the fear that in another close election, Nader (who announced his pick for vice president this week) could once again play a decisive role as a third-party candidate in crucial swing states - much as he did in Florida in 2000, where he won some 97,000 votes as Mr. Gore lost the state by less than 600 votes.
"I think Nader is scaring the bejeebies out of the Democrats," says Stu Rothenberg, editor of the Rothenberg Political Report, a newsletter. "They have nightmares of 2000 all over again."
The result is an unusual political scenario, in which there is an organized effort to stop a third-party candidate - something never confronted by Ross Perot, who started the Reform Party in 1992 and won nearly 20 percent of the vote in that year's presidential race.
What's different in Nader's case, say experts, is the unique circumstances of the 2000 race - which was ultimately decided by the Supreme Court - and the very changed, and politically charged, political landscape of 2004, which has filled many Democrats with an almost missionary "anybody but Bush" zeal.
Many prominent "progressives" who supported Nader in 2000, including documentary filmmaker Michael Moore and Ben and Jerry's cofounder Ben Cohen, won't be supporting Nader this time. Even The Nation magazine, which has had a long relationship with the anticorporate crusader, editorialized against him running.
For his part, Nader is undaunted. "A lot of liberals have abandoned us," he acknowledged in a recent phone interview. "And it will be hard to get them back. They've reached a point of desperation where their expectation level is even lower. That's too bad.