Unity08, which attracted actor Sam Waterston to be its spokesman, was aiming to get on state ballots, an exhaustive process for a third party. The plan was to create an alternative bipartisan presidential ticket that was to be chosen online later this year.
Organizers said in a letter to supporters that they were halting the ballot access project but said all was not lost - themes of bipartisanship and political unity are starting to catch on.
"We have accomplished a major portion of what we set out to do," the letter said. "But in the specifics and logistics, we have fallen short."
Organizers said it was difficult to rally millions of people to support a process rather than a candidate. Also, the group was subject to Federal Election Commission rules and was limited to $5,000 contributions from individuals, which it said limited fundraising potential.
The operation was founded by independent Angus King, the former governor of Maine; Hamilton Jordan and Gerald Rafshoon, former aides to President Carter, and Doug Bailey, a former staffer on President Ford's 1976 campaign.
Bailey and Rafshoon have already left, the letter said, to form a committee to draft Mayor Michael Bloomberg into the race. Bloomberg, a billionaire independent, says publicly he is not a candidate but is gathering extensive research to assess his viability.
Unity08 is not shutting down, its organizers said. It is challenging the FEC rules in court and plans to keep its presence on the Web in case the situation changes this spring.