You screwed up. Secretary Vilsack may have been the one who executed the decision, but the buck stops at your desk. Cabinet secretaries don't work in a vacuum. Even if you were never consulted on a decision, the decisions they make are done with the full imprint of your office. The decision to fire Shirley Sherrod was a mistake, and it happened with your authority.
The clear mistake made was believing the lies and presentation of serial liar Andrew Breitbart and his allies at Fox News Channel. Bluntly, this was stupid. You should know better. The right wing is built on a foundation of lies and deception. If a figure on the right is speaking, it's safe to assume that they are not telling the truth. I understand your belief in bipartisanship and reaching across the aisle, and I even support it (within reason) but especially when it comes to right-wing media figures, it is a fools errand of the worst sort for you or your cabinet to have invested anything in their words.
This was wrong, sir. This video and your actions smeared a public servant's name. Shirley Sherrod is the kind of person whose service deserves reward, not to have her name dragged through the right wing mud with the aid of the highest office in the land.
The only honorable thing for your administration to do is to offer Ms. Sherrod her job back (I doubt she would take it under the circumstances, but she deserves for an offer to be made) and an apology from Secretary Vilsack and yourself.
If these steps aren't taken, at best we'll have to assume that the right wing media is now the final voice on who can and cannot serve in our government, based on falsified evidence that smears their name. When we voted for you, it was most certainly not a vote to give Andrew Breitbart hiring and firing power in our government.
This mistake lies at your feet. Enemies of the presidency and the American government have been enabled, while faithful public servants have been attacked. Please remedy this problem, quickly.