Illustrating the struggles of defining the limits of presidential privilege, one former White House aide gave conflicting answers Wednesday to a Congressional committee investigating the firing of nine U.S. attorneys, and a second refused to testify at a hearing on the same topic today.

Former White House Political Director Sara Taylor struggled to define the boundaries of what she could and could not say to the Senate Judiciary Committee on Wednesday, in several cases first declaring that she could not answer questions because of a White House assertion of executive privilege, then later answering the questions anyway.

Ranking member Arlen Specter (R-Pa.) suggested during the hearing that Taylor’s appearance “might serve as a prototype to try to get some information from other people in the White House who could testify without going into executive privilege,” but the White House apparently is not convinced.

George Manning, the attorney for former White House counsel Harriet Miers, informed the House Judiciary Committee that she had been instructed by the president not to appear at that panel’s hearing today.

In a July 10 letter released by the committee Wednesday, White House counsel Fred Fielding told Manning that Miers “has absolute immunity from compelled congressional testimony as to matters occurring while she was a senior advisor to the president.”

Fielding was citing a July 10 Justice Department legal opinion signed by Principal Deputy Attorney General Steve Bradbury, which maintained — quoting then-Attorney General Janet Reno — that forcing a senior presidential adviser to testify “would be akin to requiring the President himself to appear before Congress on matters relating to his constitutionally assigned functions.” Therefore, Fielding wrote, “the president has directed [Miers] not to appear at the House Judiciary Committee hearing.”

Fielding had previously said the president would assert executive privilege over the testimony of both Taylor and Miers, and House Democrats said they anticipated that Miers would assert that privilege on a question-by-question basis, as Taylor did Wednesday.

But Taylor’s performance highlighted the pitfalls of that approach.

Early in Wednesday’s hearing, Senate Judiciary Chairman Patrick Leahy (D-Vt.) asked Taylor whether she had discussed the firing of the U.S. attorneys with President Bush, whether she had been in meetings with Bush where the firings were discussed and whether she had seen any decision documents for the president about the firings. She refused to answer all three questions, saying, “I have a very clear letter from Mr. Fielding, and that letter … asks me to follow the president’s assertion of executive privilege. And as I read that, I determined my acknowledging whether a conversation occurred or did not occur would in fact be part of the deliberations.”

But a few hours later, Leahy asked the same questions, and Taylor answered them. She never discussed the firings with the president, was never in a meeting with him where the firings were discussed and is “not aware of a presidential decision document,” she said.

Sen. Benjamin Cardin (D-Md.) and other Democrats suggested Taylor was answering questions that reflected well upon the White House but was using Fielding’s privilege claim as an excuse to avoid providing embarrassing answers. “I think she has been very selective in her use of privilege,” Cardin said.

Taylor was being advised by her attorney on the assertion of privilege, but several sources said she was not being advised by anyone from the White House.

Leahy said he has not ruled out the possibility of pursuing a contempt citation against Taylor for refusing to answer some questions, but he also said he had not made a decision yet. Leahy said he would take the transcript to his home in Vermont over the weekend before making a decision on next steps.

Specter attempted at the end of the hearing to protect Taylor from a contempt citation by leading her through a series of questions in which she said she was refusing to answer some questions only because of the White House assertion of privilege, and that she would be happy to come back and be more responsive if the White House would waive the restrictions on her.

Specter and Leahy both raised concerns about limits that the White House has placed on testimony by top officials, saying that the administration is offering only to allow off-the-record conversations with a limited number of Senators and with limited opportunities for follow-up.

But White House spokesman Tony Fratto said the White House has been more flexible than Congress.

“We are the only ones who have offered terms,” Fratto said. “They started with, ‘You must come testify,’” and the White House response was “‘Here is an offer that goes beyond our obligation.’ They come back with ‘You must come testify.’”

House Judiciary member Chris Cannon (R-Utah) supported the White House decision and said, “This investigation continues to linger among us like a rumor that just won’t die.”