From Thinkprogress-
http://thinkprogress.org/2007/03/20/white-house-testify/Senate Judiciary Chairman Pat Leahy (D-VT) has called on Karl Rove and other top White House aides to testify under oath in front of Congress concerning their role in the U.S. attorney purge. A response from White House Counsel Fred Fielding is expected today, but in the meantime, the White House and its allies have put up a fight, arguing that presidential advisers have historically not testified in front of Congress:
White House Press Secretary Tony Snow: Well, as you know, Ed, it has been traditional in all White Houses not to have staffers testify on Capitol Hill. <3/13/07>
White House Counselor Dan Bartlett: I find it highly unlikely that a member of the White House staff would testify publicly to these matters. <3/13/07>
House Minority Leader John Boehner (R-OH): No, I think you’re violating a precedent there that should not be violated. … I believe that under the separation of powers, there are limits to the extent to which Congress can subpoena or demand testimony from those who were closest to the president. <3/15/07>
But in reality, there is no such precedent.
According to the Congressional Research Service, under President Clinton, 31 of his top aides testified on 47 different occasions. The aides who testified included some of Clinton’s closest advisors:
Harold Ickes, Assistant to the President and Deputy Chief of Staff - 7/28/94
George Stephanopoulos, Senior Adviser to the President for Policy and Strategy - 8/4/94
John Podesta, Assistant to the President and Staff Secretary - 8/5/94
Bruce R. Lindsey, Assistant to the President and Deputy Counsel to the President - 1/16/96
Samuel Berger, Assistant to the President for National Security Affairs - 9/11/97
Beth Nolan, Counsel to the President - 5/4/00
In contrast, between 2000 and 2004, Bush allowed only one of his closest advisers, then-Assistant to the President for Homeland Security Tom Ridge, to appear in front of Congress. He has also refused three invitations from Congress for his aides to testify, a first since President Richard Nixon in 1972. Clinton did not refuse any.