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The chairman of the Senate Judiciary Committee served notice Wednesday he intends to question Harriet Miers about the Bush administration's policy of detaining suspected terrorists at Guantanamo Bay (search), injecting new uncertainty into a Supreme Court nomination already in doubt.

In a letter to Miers, who is White House counsel, Sen. Arlen Specter (search) also said he would ask what assurances she could offer that she would be independent, if confirmed, "and not give President Bush any special deference on any matter involving him that might come before the court."

Specter, R-Pa., released the letter as the White House (search) struggled to build support for an appointment that has drawn withering criticism from some prominent conservatives outside Congress and steady skepticism — or worse — from Republican senators.

Three GOP officials said they no longer felt certain that Miers' troubled nomination would survive as long as the Nov. 7 target date for hearings, and that a withdrawal was not out of the question. They spoke on condition of anonymity, noting that the administration's official policy is one of strong continued support for the president's pick.

A conservative group that had given Miers the benefit of the doubt changed positions on Wednesday. Concerned Women of America (search), which had so far supported Bush's judicial nominees, urged the president to withdraw her nomination.

"We wanted to back the president, and sought evidence to support this nomination, but we find this Supreme Court nominee unqualified and her record troubling," said Beverly LaHaye, the group's founder. "However, we look forward to a nomination that we can wholeheartedly endorse."

Miers met with Sen. David Vitter, R-La., the latest in a round of senatorial courtesy calls, and labored to answer written questions from the Judiciary Committee (search) by day's end. The panel sought the information after deeming her earlier responses incomplete.

Vitter told reporters he wanted the White House to provide written evidence that Miers has a conservative judicial philosophy. "What I am suggesting is that I'd love to see more written material that predates the nomination," he said.

Miers was named less than a month ago to replace Justice Sandra Day O'Connor (search), whose views on the constitutional questions of the most contentious issues of the day often left her as the pivotal vote on 5-4 rulings. In particular, O'Connor joined in rulings that upheld abortion rights and affirmative action.

While several GOP senators have lamented the shortage of material detailing Miers' views, a speech she delivered in 1993 drew attention from Vitter and other conservatives.

Discussing the issues of abortion and voluntary school prayer, she told the Executive Women of Dallas (search), "The underlying theme in most of these cases is the insistence of more self-determination. And the more I think about these issues, the more self-determination makes the most sense."

Vitter declined to tell reporters what Miers had told him about the speech she made a dozen years ago. Sen. Sam Brownback (search), R-Kan., said it raised another question in his mind about her views. "It's something we'll have to probe," he said.

Specter's letter set out a controversial area he intended to probe — the constitutional underpinnings of the administration's handling of suspects in the global fight against terrorism.

Referring to cases involving the detainment of "enemy combatants" at a U.S. facility at Guantanamo Bay (search), Cuba, Specter noted that the administration contends that most of the detainees are kept in custody "not for punishment" but to keep them for interrogation and prevent them from returning to the battlefield.

"Are there any limitations as to how long detainees may be held for the purposes identified by the government?" he asked, setting out the first in a series of questions he intended to pose at the hearings. Pentagon policy on the issue makes no mention of a time limit on the detentions.

Additionally, Specter posed a series of questions about the authority of the president to detain aliens outside U.S. borders.

These questions all appeared to involve controversy for Miers, since she has advised Bush privately about the war on terror, and the president has long insisted that advice offered within the White House is off-limits to outsiders.

The issues raised by the cases that Specter cited may resurface at the Supreme Court (search) in the future, and nominees traditionally have shied away from offering opinions in such circumstances. Chief Justice John Roberts (search) invoked that precedent numerous times at his own confirmation hearings.

Specter also outlined questions relating to Congress' constitutional authority to declare war.