Because they really aren't that smart and they really are that used to the media covering for them.
I think that's the answer. Just as Obama's been carried aloft all his adult life on affirmative action.
SCalGal has it exactly right.
The left has such tight bonds of collusion, they truly believe they are above the law and that they can paint any lie as truth and it will be reported as such until it is accepted as such.
An additional point is this, as anti-PC as it is: Obama has made a career out of exploiting the unjust system in this country that is Affirmative Action. In addition to the above points, he truly believes everyone will give him a “pass” on anything because he is the “first black president.”
Unfortunately, there are many leftists in this country that are exploiting that to further their communist/socialist agenda and many others on the left who will simply toe that line in order to be viewed as “good” by the PC.