The White House moved toward a showdown in court with the Democratic-led Congress today by refusing to provide demanded information and testimony in an investigation into the firing of prosecutors.
In a letter to congressional leaders, White House counsel Fred Fielding called their demands "unreasonable because it represents a substantial incursion into presidential prerogatives."
President George W. Bush has adopted a legal doctrine known as executive privilege that has been occasionally invoked with mixed success throughout U.S. history to shield presidents and their aides from having to answer questions or turn over information to Congress or grand juries.
Democrats in Congress want the information and testimony to determine if the firing of nine federal prosecutors last year was the result of partisan politics and White House efforts to reward supporters.
Democrats made it clear they intend to go to court to challenge Bush's claim and decide which branch of government was in the right.
However, House Judiciary Committee Chairman John Conyers said the courts would decide on the validity of the invocation of executive privilege and not the White House.
"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," the Michigan Democrat said in a statement.
In his letter, Fielding rejected requests for materials to support Bush's claim of executive privilege last month. He also wrote Bush, as expected, was asserting presidential privilege for the second time to block subpoenaed testimony by two former aides, Sara Taylor and Harriet Miers.
Taylor, who served as White House political director, has been summoned to testify before the Senate Judiciary Committee on Wednesday, while Miers, who served as White House counsel, had been ordered to testify before a House panel on Thursday.
There was no immediate indication when Democrats would go to court.
Bush and US Attorney General Alberto Gonzales insist the dismissals of the federal prosecutors were justified but mishandled. Gonzales, with Bush's support, has withstood bipartisan calls to resign.
Investigators have questioned if partisan politics played a role in the firings, and have said it appears that in at least some cases a US attorney may have been dismissed to influence a politically sensitive criminal investigation.