Nearly 18 months after images of abuse at Iraq's Abu Ghraib prison stunned the world, the US Senate voted Wednesday to clarify rules that govern the military's treatment of detainees.
The amendment's overwhelming passage, despite objections from the White House, marks a rare congressional challenge to President Bush as commander-in-chief at a time when public support for his presidency is at a low.
It also puts Congress on record demanding a standard of humane treatment for detainees, even in the context of an all-out war on terror.
In the end, what tipped the vote was a call for clarity.
"We have to clarify that this is not what the United States is all about. This is what makes us different from the enemy we are fighting," said Sen. John McCain (R) of Arizona, who sponsored the amendment that bars cruel and inhumane treatment of detainees.
In the run-up to the vote, Senator McCain, who survived years of torture during the Vietnam War, read a letter to his colleagues from a young Army captain, a veteran of Afghanistan and Iraq, who wrote that he repeatedly tried to get answers from his chain of command on what standards apply to the treatment of enemy detainees - and got no answers.
Nor did senators, who peppered panels of top military officials with the same questions in a series of hearings since reports of abuse at Abu Ghraib and Guantánamo first surfaced.
"If the Pentagon's top minds can't sort these matters out, after exhaustive debate and preparation, how in the world do we expect our enlisted men and women to do so?" asked McCain, before the Senate passed the measure in a 90-9 vote.
White House officials say that legislation would limit the president's ability to carry out the war on terrorism. But military analysts say that thought is shifting on the value of torture in venues like Iraq.
"The practical reality is that the attitudes of Sunni Arabs towards US forces, and their image of how they treat Iraqis, is at least as important as any given tactical encounter," wrote Anthony Cordesman of the Center for Strategic and International Studies, in an issue brief on the impact of detainee rights on the war on terror.
"What may initially seem like a 'tactical necessity' [torture or ill-treatment] can actually create more hostility and violence in ways that kill or wound hundreds of Americans, aid the insurgency, and prolong the fighting."
For months, the White House has threatened to veto such an amendment, now attached to the $445.5 billion Defense Appropriations bill for fiscal year 2006. The amendment was initially attached to the 2006 Defense Authorization bill, but was pulled from the Senate floor by Senate majority leader Bill Frist, after the White House threatened a veto.
McCain's amendment establishes the Army Field Manual as the uniform standard for interrogation of detainees and prohibits "cruel, inhumane, and degrading treatment of prisoners in the detention of the government."
But defense analysts note that such a provision would not cover the Central Intelligence Agency or curb the process of moving detainees to other countries where torture is allowed, limiting its impact.
"They've left the door open for the CIA. The really hard stuff is still authorized by the president," says Christopher Pyle, a military legal analyst at Mount Holyoke College in South Hadley, Mass.
The military insists that its rules for interrogation are not inhumane, and recent investigations into detainee abuse suggest some progress. Members of Congress who have toured the detention facility at Guantánamo Bay this year have generally offered praise.
But the fact that there are no established guidelines codifying humane and acceptable treatment has led to concern in some quarters of the Pentagon.
Officially, the Pentagon claims that enemies captured in the war on terror are different from enemies captured in conventional wars. In this more open-ended and uncertain war, officials say, it is important not to limit the tools interrogators can use.
"I believe we are seeing the beginning of a crusade against freedom from the militant terrorist Islamic entities throughout the world," said Sen. Ted Stevens (R) of Alaska, opposing the amendment. "If this amendment passes, the United States will not have effective control of those people."
Yet some within the military establishment worry about opportunities for abuse, and also the confusion that can arise from ambiguity. In a culture built on rules and order, the lack of defined standards leaves soldiers in legal limbo.
In his first policy statement since resigning as secretary of State, Colin Powell urged Congress to use its constitutional powers to clarify treatment of detainees.
While some Democrats saw the vote as a rebuff of the president's conduct of the war, Republicans say it is limited to the treatment of detainees and human rights.
"It was one of those rare moments when the conscience of the Senate spoke loud and clear over both partisanship and ideology," says Marshall Whittman, a former spokesman for Senator McCain, now with the Democratic Leadership Council.
The Senate bill must now be reconciled with the House version, which includes no such provision on detainees.