In the 2000 US presidential election Ralph Nader won nearly three million votes on the Green party's ticket. Running in 43 US states, his campaign called for economic justice, universal health care, affordable housing, workers rights and tougher gun laws.

He rejected criticism he had taken away votes from the Democrats' Al Gore and helped the Republicans' George W Bush win saying: "You can't spoil a system that's spoiled to the core". And he predicted the Greens would emerge as a powerful democratic force.

But in subsequent elections, the Greens won just a fraction of the 2000 vote. They are due to select this year's candidate in July. Their policies are well to the left of the mainstream calling for an economic bill of rights which offers all workers a proper living wage. They accuse the Democrats and Republicans of placing the interests of Wall Street first.

They also emphasise comprehensive healthcare, education and housing as well as proper services for the elderly. Plus a fundamental shift in environmental policy - from breaking the addiction to oil to what it calls a World War II scale change in the way energy is produced and spent.

And the political terrain could not be more difficult. Barack Obama is on the defensive over high gas prices and drilling and he has been accused of putting the environment ahead of jobs.

What can the Green party do to influence the general election? And how can it - or any other third party - break the stranglehold of the two party system? Plus, how important will energy and environmental issues be in 2012?

To discuss these issues presenter Anand Naidoo is joined by Tim Dickinson from Rolling Stone magazine; Scott McLarty from the Green party; and Myron Ebell, the director of energy and global warming policy at the Competitive Enterprise Institute and a prominent climate change sceptic.