When did Obama know about Ayers terrorist background?

Lynn Sweet of The Chicago Sun-Times reports:

So, did he know who Ayers was when he went to his home in 1995?

"My understanding is that when he went there, he did not," Axelrod said.

Reporters noticed that clause -- "my understanding is" -- and pressed further. Did Axelrod ask Obama if he knew Ayers' history when he first met with him?

"Yes," Axelrod said.

And he did not know?

"Yes," Axelrod said. "That's what I've said -- I answered the question when I was asked the other day. But no one's suggesting that he never knew. I mean that's not -- we weren't offering that. I wasn't offering it -- I was asked a question that you just asked me and just answered it. I wasn't making an argument about it."

David Axelrod's understanding.