Rush Limbaugh wonders why Barack Obama doesn't get blamed for anything. It's racism, plain and simple. Whites are afraid to hold blacks to the same standards as they hold whites. Barack Obama came along at just the right time in American history: when white guilt reached a fever pitch. He was elected by guilty whites; he was reelected by guilty whites; and he is given a free pass by guilty whites. Don't take my word for it. Read Shelby Steele.
Addendum: There are two forms of white racism. The first consists in holding blacks to higher standards than whites. It is motivated by malevolence. The second consists in holding blacks to lower standards than whites. It is motivated by guilt. Barack Obama is the beneficiary of the second type of white racism. It's what Michael Gerson called "the soft bigotry of low expectations."