It's not just any one person, nor is it just white liberals. It is the demonization of Black Republicans by the entire Liberal establishment.
"I don't think I realized Ben Carson was conservative until last month. Shame he's becoming the right wing's go-to black token."
Tweet by Deen Freelon (Black American University Professor)(@dfreelon) March 16, 2013
Also, examine Liberal attitudes towards Herman Cain during the GOP primaries.
How about liberal attitudes towards Michelle Bachmann, Newt Gingrich, Rick Santorum, Rick Perry, Mitt Romney?
Did liberals go easier on those people because they were white?
No, they were White Racist Republicans (according to Liberals) Palin and Bachmann were apparently women in the wrong party. Gender, along with race was the factor there. Liberals painted the four men you listed as misogynistic, racist, "anti poor" people.
There were a lot of things for them to be targeted for other than being white. However, if anyone on the Left were these things, they could get away with just about anything. Criticize Hillary or Michelle? You hate women and are racist. Criticize Obama? You're racist. Say that Trayvon Martin started the fight that got him killed? You're racist.
In fact, Liberals are harder on the other side than they are on themselves! They fail to acknowledge their own racist tendencies but don't hesitate to point them out in others.
Nice trap question by the way.