On August 1, 2007, Bush invoked the privilege for the fourth time in little over a month, this time rejecting a subpoena for Karl Rove. The subpoena would have required Rove to testify before the Senate Judiciary Committee in a probe over fired federal prosecutors. In a letter to Senate Judiciary chairman Patrick Leahy, Fielding claimed that "Rove, as an immediate presidential advisor, is immune from compelled congressional testimony about matters that arose during his tenure and that relate to his official duties in that capacity."