Ralph Nader denounced President Obama's lack of leadership on Monday and said he was leaning against, but would not rule out, a 2012 presidential bid.

In a radio interview with liberal activist Mark Green, Nader said that Obama had resorted to "mealy-mouthed, well-composed rhetoric" on the BP oil spill but hasn't backed it up with real action, like banning BP from doing business with the government.

He added that a stubborn Congress is no excuse for not passing a strong climate bill.

"That's a cop out. Would LBJ not be able to get it through when he had 59 Democrats and an independent? [Obama] doesn't know how to deal like LBJ did. He doesn't have that fervor," Nader said. 

As for his own 2012 prospects, Nader said he would rather have another liberal run in his place but would not rule out the possibility of a fifth presidential campaign.

"I want the progressive agenda to be on the ballot. I'd rather have someone else do it like Jim Hightower or Mark Green," Nader said.

Green chuckled and said he "probably" would not be on the ballot.