'Privilege'
 
Presidents have used executive privilege in the past to withhold information from congress on the grounds that aides will not give them candid advice if they know they may be required to testify.
 
"You may be assured that the president's assertion here comports with prior practices in similar contexts, and that it has been appropriately documented"

Fred Fielding, White House counsel
In a letter to the heads of the House and Senate Judiciary panels, Fred Fielding, White House counsel, insisted that Bush was acting in good faith and refused legislators' demand that the president explain the basis for invoking the privilege.
 
Regarding subpoenas the judiciary panels issued, Fielding said: "You may be assured that the president's assertion here comports with prior practices in similar contexts, and that it has been appropriately documented."
 
John Conyers, the Democratic House chairman of the judiciary panel, in a written statement, said: "Contrary what the White House may believe, it is the congress and the courts that will decide whether an invocation of Executive Privilege is valid, not the White House unilaterally."
 
Testimony
 
The privilege claim on testimony by former aides will not necessarily prevent them from testifying this week, as scheduled.
 
Patrick Leahy, the Democratic Senate chairman, said that Taylor may testify as scheduled before the Senate panel on Wednesday.
 
The House Judiciary Committee scheduled Miers' testimony for Thursday, but it was unclear whether she would appear, according to congressional aides.
 
The exchange on Monday was the latest step in a slow-motion legal dance between the White House and legislators toward eventual contempt-of-congress citations. If neither side yielded in that circumstance, it would go to a federal court.
 
The probe into the US attorney firings was only one of several Democratic-led investigations of the White House and its use of executive power spanning the war in Iraq, Bush's secretive wiretapping program and his commutation last week of a prison sentence for a former senior aide to Dick Cheney, the US vice-president.