According to this AP article
there's no legal reason that Condi can't testify under oath.
It is rare for White House advisers to testify publicly before Congress or congressionally appointed panels like the Sept. 11 commission. But exceptions exist, and legal scholars say they poke holes in Rice's argument.
It might be different if Condi had been closed lipped from the outset, but as she's talked to everyone who didn't want to put her under oath, her insistence on not raising her right hand seems suspect.
The whole idea of executive privilege is that the president's advisers should be able to give advice in confidence," said Herman Schwartz, a constitutional law professor at American University. "That means the advice should be kept confidential. But she's talked to everybody under the sun.
And as to Condi's claim that no national security advisor had testified before congress? That's more than suspect, it's just plain wrong.
There are several instances in which sitting national security advisers or White House aides testified before legislative bodies. Among them:
Zbigniew Brzezinski, national security adviser to then-President Carter, testified before the Senate in 1980 regarding alleged lobbying or criminal activities by the president's brother, Billy Carter, on behalf of Libya.
Sandy Berger, national security adviser to then-President Clinton, testified in 1997 before a Senate committee reviewing the Clinton campaign's fund-raising practices.
Several presidential aides during the Nixon administration testified before the Senate about Watergate, including White House counsel John Dean, former chief domestic adviser John Ehrlichman and former White House aide H.R. Haldeman.
So, is there any legitimate reason remaining why she won't take the stand?