"how could he ever have associated himself with Bill Ayers? Or Rev Wright or Rezko?"

Because finding out Ayers background was not an ISSUE when they were both on that board together. He didn't 'hang out' with Ayers....he did not even 'associate' with Ayers in the sense the slimers are trying to portray it.

Rev. Wright married the Obamas, and was just a nice preacher to them for many years. He didn't 'choose' Wright based on his extreme statements, and he disavowed those when he realized what had been said...(he was **NOT** in church the day that famous statement was made.)
Rezko: He met Rezko before there was a problem...then...

"U.S. Sen. Barack Obama expressed regret late Friday for his 2005 land purchase from now-indicted political fundraiser Antoin "Tony" Rezko in a deal that enlarged the senator's yard.

"I consider this a mistake on my part and I regret it," Obama told the Chicago Sun-Times in an exclusive and revealing question-and-answer exchange about the transaction.

In June 2005, Obama and Rezko purchased adjoining parcels in Kenwood. The state's junior senator paid $1.65 million for a Georgian revival mansion, while Rezko paid $625,000 for the adjacent, undeveloped lot. Both closed on their properties on the same day.

.....

""With respect to the purchase of my home, I am confident that everything was handled ethically and above board. But I regret that while I tried to pay close attention to the specific requirements of ethical conduct, I misgauged the appearance presented by my purchase of the additional land from Mr. Rezko," Obama said.

"It was simply not good enough that I paid above the appraised value for the strip of land that he sold me. It was a mistake to have been engaged with him at all in this or any other personal business dealing that would allow him, or anyone else, to believe that he had done me a favor," the senator said. "