In 2000 Ralph Nader cast his solid for George W. Bush. He should have, at the very least, made a push to have been Bush's running mate. As VP, Nader couldn't have been any worse than Dick Cheney.
In 2004, again he backed George W. Bush against John Kerry, but this time the Green Party refused to lend him their backing.
In 2008, Nader has indicated that he prefers John McCain to either Hillary Clinton or Barack Obama, runnning this time, I'd assume on the Nader Party ticket.
Maybe this time Nader should forge an allegiance with Joe Lieberman and start the Liberman/Nader Election Spoiler Party.