We're talking about Ralph Nader, who was already known for his car safety advocacy by the POD and advocacy of third parties by the late '70s.Let's not fall for Kucinich's mythologizing of his past. He got elected mayor of Cleveland by playing the ethnic card and had a term so disastrous it put an end to his political ambitions for years to come, until he reinvented himself as a liberal (and a pro-life one at first). Even if he wasn't a spent force, he's politically closer to Wallace (shock!) than Dellums.
Anyways, Kucinich's leftwards tilt probably has something to do with the fact that after being kicked out of the Mayor's Office, he sunk into debt and poverty.