US:President George Bush has escalated a showdown with Congress over presidential power by blocking the testimony of two former White House aides about the controversial firing last year of nine federal prosecutors.
Judiciary committees in both houses of Congress have subpoenaed former White House counsel Harriet Miers and former political aide Sara Taylor to testify in investigations into claims that the prosecutors were fired for party political reasons.
In a letter to the committee chairmen yesterday, however, White House counsel Fred Fielding said that "the president feels compelled to assert executive privilege" to prevent the two women from testifying.
Executive privilege is the power US presidents and other members of the executive branch of government invoke to resist searches and other interventions by the legislative and judicial branches.
Last month, Mr Bush asserted executive privilege in refusing to hand over to Congress White House records related to the firings, causing Senate judiciary chairman Patrick Leahy and his counterpart in the House, John Conyers, to question the legal basis of the assertion.
In yesterday's letter, Mr Fielding refused to list the documents the president was withholding, saying Congress had no right to know what they were.
"We are aware of no authority by which a congressional committee may 'direct' the executive to undertake the task of creating and providing an extensive description of every document covered by an assertion of executive privilege," he wrote.
Mr Leahy said he expected Ms Taylor to testify before his committee as scheduled tomorrow, regardless of the White House letter and he poured scorn on Mr Fielding's refusal to list the documents the president is refusing to hand over.
"I have to wonder if the White House's refusal to provide a detailed basis for this executive privilege claim has more to do with its inability to craft an effective one," Mr Leahy said.
Mr Fielding suggested that the entire investigation into the firings was without any constitutional basis because, as political appointees, the federal prosecutors serve at the pleasure of the president. He angrily rejected a claim by Mr Leahy and Mr Conyers that the president's assertion of executive privilege belied any "good faith" attempt to determine where privilege should truly apply.
"The assertion of executive privilege here is intended to protect a fundamental interest of the presidency: the necessity that a president receive candid advice from his advisers and that those advisers be able to communicate freely and openly with the president, with each other and with others inside and outside the executive branch," Mr Fielding wrote.
Mr Conyers, who has threatened to hold the White House in contempt of Congress if the administration does not co-operate with his investigation, said he was disappointed with the president's decision to escalate the conflict.