Cain has inevitably drawn attention as the only African-American in the field. And, as a black Republican linked to the Tea Party -- a movement often accused of racial animosity toward Barack Obama -- he has become a magnet for a peculiar left-wing brand of race-baiting.

One notorious display of this attitude occurred earlier this month on the MSNBC program "The Last Word," when host Lawrence O'Donnell berated Cain for his failure to participate in the civil rights protests of the 1960s as a teenager and young adult in the South.

In his just-published autobiography, Cain writes that he and his brother would reluctantly move to the back on the bus when told to do so by the driver, minding their father's admonition to "stay out of trouble." Where, O'Donnell sarcastically inquired, would blacks be now if Rosa Parks had followed such advice? When Cain reasonably replied that his father's advice was not to Rosa Parks but to his high school-age sons, O'Donnell went on to push him on his lack of activism in college.

Even many left-of-center observers, such as Mediate.com columnist Tommy Christopher, were aghast at the spectacle of a white liberal smugly chiding a black man for the personal choices he made in a very difficult time. (Those choices included breaking down professional barriers by going to graduate school and pursuing a career in computer science.) What's more, as MSNBC commentator Melissa Harris Perry noted, there is a blatant double standard at work: white politicians of Cain's generation are not grilled on what they did in the civil rights movement. Bill Clinton, often praised for his unique ability to connect with African-Americans, attended college at the same time as Cain and worked as an intern in a segregationist senator's office.

Nonetheless, some left-wing blogs have cheered O'Donnell's supposed takedown of Cain -- and others have peddled even nastier fare.