If Nader decides to run, his late start, lack of party affiliation - he won't be on the Green Party ticket this time - and the challenge of getting his name on ballots in 50 states weigh against his candidacy.
So does the palpable anger among many Democrats after nearly four years of a Republican in the White House.
Calling Nader "egomaniacal," veteran Democratic strategist Dane Strother said the independent would "have the same impact he had last time. He would hand the presidency to George Bush."
Democratic National Committee chairman Terry McAuliffe said he met with Nader several times urging him not to run because he could pull votes from the Democratic nominee.
"I don't want Ralph Nader's legacy that he got George Bush for eight years in this country," McAuliffe said on CNN. "I'm urging everybody to talk to Ralph Nader. I'd love him to take a role with our party, to energize people, to get out there and get the message out."
After weeks of postponing his decision, Nader will appear on NBC's "Meet the Press" to make the announcement, said Linda Schade, a spokeswoman for Nader's presidential exploratory committee. Schade declined to say what the decision would be, but said Nader would be available for interviews following the television appearance and he planned to hold a news conference Monday.
The prominent staging of his announcement, following months of active fund raising, suggests Nader, who turns 70 next week, is ready to take his progressive agenda directly to the voters, despite Democratic grumblings that he would only be helping President Bush secure another term.
As the Green Party's nominee in 2000, Nader appeared on the ballot in 43 states and Washington, D.C., garnering only 2.7 percent of the vote. But in Florida and New Hampshire, Bush won such narrow victories that had Gore received the bulk of Nader's votes in those states, he would have won the general election.
In six other states that Gore won - Iowa, Maine, Minnesota, New Mexico, Oregon and Wisconsin - Nader received more votes than Gore's margin of victory, making those races even closer for the Democrats.
Despite being described by some as a spoiler, Nader for months has been gauging support for another run through an Internet site and exploratory committee. On Thursday, he sent Web site subscribers an e-mail asking them for their thoughts on whether he should seek the presidency.
Nader shrugs off the spoiler moniker, saying a large portion of his supporters would not have voted at all and some would have gone for Bush.
According to exit polls at the time, 47 percent of Nader voters said they would have voted for Gore if only Gore and Bush had been on the ballot, 21 percent would have backed Bush and 30 percent said they would not have voted. The poll on Nader voters had a sampling error of plus or minus 8 percentage points.
The campaign of Democratic front-runner John Kerry said the Massachusetts senator and Nader stand together on many issues and stressed the importance of party unity.
"Americans who want to see change in this nation know how important it is to defeat George W. Bush," a campaign statement said. "To do that, it is important that we remain united in November and rally behind the Democratic nominee, whoever that may be."
Aides to rival candidate John Edwards declined to comment on a possible Nader run.
Nader has decided not to seek the Green Party's nomination this time and party officials have expressed doubts he would get on many state ballots without a party organization and so late in the political season.
Richard Winger, editor of Ballot Access News, a monthly publication that discusses state ballot access laws, said an independent candidate would need about 700,000 signatures to get on the ballots of all 50 states, a massive undertaking requiring millions of dollars and hundreds of grass-roots supporters. Nader had raised about $100,000 by the end of December.
But it is possible. John Anderson, who ran as an independent in 1980, didn't decide to do so until April 23, 1980, and he managed to get on the ballot in all 50 states. This year, the Green Party expects to get on 35 to 40 state ballots, said Ben Manski, a party co-chairman.
Nader's impact on the 2000 race left some feeling bitter, and many former supporters are now urging him not to run. Two former Nader boosters in Colorado have founded a Web site for repentant Nader voters. Another site, urging Nader not to run, has had 135,000 visitors since it debuted in January, according to founder John Pearce, who identifies himself as a Democrat.