This was done a number of years ago, not long after the Senator Larry Craig toe tapping incident.  I think today Jerry Eversole and Roger Clemens come to mind when you think of those who should follow the advice of Supreme Court Justice Robert Jackson.  James Duane is a law school professor who put this together for a class he teaches.  His focus was on the police, the advice is the same for a grand jury.  You be the judge of the importance of not testifying before a politically motivated grand jury.

http://www.youtube.com/watch?v=i8z7NC5sgik