Color me skeptical. We can't keep secrets that should remain secret under wraps in this country for more than three days.
Even if there is a damaging a video of Michelle, he'll just throw her under the bus like he has everyone else who has become a problem.
What information comes to be public perception, and how it gets there, is a study in its own right. There are plenty of "public secrets." Politicians are particularly protective of their personal privacy (including, in many cases, their deeply held allegiances and alliances), as are members of the media.
Reflect on the number of times "surprising" news has come out. Cunningham's being a bought man, Congressional pages being courted by congressmen ... I won't be surprised to find evidence that Michelle Obama either subscribes to or echos the black liberation rhetoric of Rev. Wright and Fr. Pfleger.