The battle between the executive and legislative branches stems from the row over the eight federal prosecutors who were dismissed last November in what Democrats say is a blatant example of political meddling in the judicial system by the White House. The affair already threatens to bring down attorney general Alberto Gonzales, accused of turning a blind eye as Karl Rove and other White House officials schemed with their opposite numbers at the justice department to remove the prosecutors.

But the affair has gained a new dimension with evidence that Rove and some of his colleagues may have deliberately used Republican Party email accounts instead of the White House system to send messages relating to the attorneys and other controversial issues. The messages, Democrats suspect, may have been deleted, circumventing rules that White House and government emails must be preserved.

The White House insisted every effort was being made to recover the missing emails. But that did not satisfy Patrick Leahy, chairman of the Senate judiciary committee, who accused the administration of lying.

"The emails are there, they just don't want to produce them, " Leahy thundered from the Senate floor. "It's like the infamous 18minute gap in the Nixon White House tapes."

The reference was to a missing crucial portion of Oval Office conversations between Nixon and his aides. The White House insisted the 18 minutes in question had been accidentally erased by Nixon's secretary, in what became known as "the Rosemary Woods stretch".