I found this quote from an old profile of Barack Obama in the May 31, 2004, issue of The New Yorker:

Jan Schakowsky told me about a recent visit she had made to the White House with a congressional delegation. On her way out, she said, President Bush noticed her “obama” button. “He jumped back, almost literally,” she said. “And I knew what he was thinking. So I reassured him it was Obama, with a ‘b.’ And I explained who he was. The President said, ‘Well, I don’t know him.’ So I just said, ‘You will.’ ”