Ralph Nader is unlikely to be a spoiler in this year's U.S. presidential race, according to a political analyst.

Ralph Nader, still seen as a spoiler by some Democrats for his bid for the Oval Office in 2000, announced a fourth run for president on Sunday. But Solon Simmons, an assistant professor at George Mason University in Virginia, told CTV Newsnet that it likely won't affect the outcome.

"Last time when Nader ran, he got less than half than a percentage point of the vote," Simmons said. "So the idea that in a vote total he's going to spoil seems unlikely."

The veteran consumer advocate made his announcement today on NBC's "Meet the Press."

Nader, who turns 74 on Wednesday, said Americans find themselves disgruntled with both the Democratic and Republican parties. He described Washington as "corporate occupied territory" where decisions aren't made in the interests of the people.

None of the current contenders for the presidency are addressing the issues of corporate crime, wasteful defence spending or labour rights, he said.

"In that context I have decided to run for president," Nader said.

Nader said Americans are disenchanted with the two mainstream parties due to the war in Iraq and economic uncertainty.

President Bush's "corporate friendly" policies have left lower and middle-income Americans in debt, he said.

Nader attacked Republican candidate John McCain as well as the Democrats' Barack Obama and Hillary Clinton for not supporting Medicare for all and for the creation of the country's "bloated" military budget.

Simmons said that where Nader can play a role is by putting pressure on the Democrats to deliver a more liberal message.

"By running again and again with a progressive message, he hopes to drive the party back toward the left, which it's been afraid to do since the democratic leadership council took power in the 80s and 90s," he said.

Nader, who has pledged to accept donations only from individuals, first ran for president in 2000 as the Green party's candidate.

That year, he captured 2.8 million votes, about 2.7 per cent of those cast.

Democrat Al Gore bested Republican George Bush in the popular vote but narrowly lost the state of Florida in a highly controversial decision.

Some Democrats have never forgiven Nader for what they saw as the siphoning of votes that allowed Bush to triumph.

In 2004, Nader's vote total fell to about 460,000 when he ran as an independent, but Democrat John Kerry lost to Bush by about three million votes.

With files from The Associated Press