The Green Party (search) and Ralph Nader (search) ran together in the past two presidential elections, but the party is going it alone this time around.

The Green Party has nominated one of its own for president for the first time, rebuffing advances from Nader for an endorsement of his independent campaign.

Members and political observers say the decision to support attorney David Cobb instead gives the party a chance to prove what it can do in a presidential race without a marquee name like Nader.

"If David Cobb is successful, it could be the single most important thing for the party," said Matt Gonzalez, who ran for San Francisco mayor last year. "It's going to be a real test of if a homegrown candidate can run for president effectively."

Cobb narrowly won the nomination Saturday.

Nader had said he would not join the Green Party and would not seek its nomination, after running under its banner in 1996 and 2000. Rather, Nader sought a formal endorsement as he tries to build support for his campaign.

Kevin Zeese, Nader's spokesman and a Green Party delegate, said the party may have jeopardized its future by turning its back on the consumer activist whose national profile helped it grow over the past eight years.

He predicted that many prominent Greens would still back Nader and that the three-time presidential candidate would still draw national media attention for his campaign while Cobb will likely be ignored.

"Often when adolescents rebel against their parents, they make mistakes. But they learn from those mistakes," Zeese said. "Hopefully, they're not mistakes that kill them."

After his nomination Saturday, Cobb said the decision was a sign that the party had emerged from Nader's shadow. But he acknowledged that it carries some risk.

Cobb said the country's electoral system is set up to ensure the failure of third parties, and predicted a hard fight to get on the ballot in many states. Cobb also said he did not expect to participate in any of the national presidential debates in the fall, and promised to protest that exclusion.

Nader was shut out of the debates in 2000 after failing to meet the 15 percent threshold in national polling and it is unlikely that Cobb will fare any better, said David Rohde, a Michigan State political science professor.

"They had very little chance even with Nader as part of the picture; with Nader out, even less so," Rohde said.