Over a single week in October, the President’s entire coalition suddenly seemed in danger of unraveling. There’s no doubt about the political import of Republican fratricide over George W. Bush’s nominating Harriet Miers to the Supreme Court, perhaps betokening the long-overdue rupture of the patronage bargain between the President and the religious right. But in global terms, the emerging chasm between Congress and the President over the Iraq War in general and war crimes in particular is of the most profound consequence–signaled by the Senate’s bracing passage, by a 90-to-9 vote, of John McCain’s anti-torture amendment to the defense appropriations bill.

The Senate’s passage of the amendment stands as a singular legislative attempt to corral Bush into compliance with international law and human rights standards. McCain’s legislation, which would prohibit the use of “cruel, inhuman or degrading treatment or punishment” by the military, bears the unmistakable moral authority of Vietnam POW McCain and Vietnam vet Senator Chuck Hagel and the strategic endorsement of more than two dozen retired senior military officers, including former Secretary of State Colin Powell and former Chairman of the Joint Chiefs of Staff John Shalikashvili. No longer can the White House pretend that for the sake of national security Congress has acquiesced in torture. The most shocking aspect of the McCain amendment is not the bill’s content but the White House’s threat of a veto in the face of near-unanimous Senate support. Even if Administration arm-twisting brings a challenge in the House-Senate conference committee, the overwhelming margin of the Senate vote sends an important message to the federal courts about legislative intent–and further isolates the Administration.

The Senate Republicans’ bout of conscience is, of course, welcome, but why so late in the war? Explain it in part by simple politics–in particular, GOP leaders’ ever more urgent need to establish an identity separate from a White House mired in scandal. But conscience is at work too, starting with an officer who witnessed the abuses and refused to remain silent. When Capt. Ian Fishback’s repeated inquiries to superior officers about torture in the 82nd Airborne Division were met with evasion or thinly veiled threats, he turned to Capitol Hill; it was his discussions with Senate aides that finally goaded the Army into ordering an investigation. He also turned to Human Rights Watch, whose subsequent report demonstrates that torture in Iraq “was systematic and was known at varying levels of command” and points out that the abuses “can be traced to the Bush Administration’s decision to disregard the Geneva Conventions” in the Afghan war. Credit, too, the cognitive dissonance experienced by Republicans like JAG reservist Senator Lindsey Graham, a bill co-sponsor, and McCain and Hagel, who make a point of quietly visiting veterans at Walter Reed Hospital every week.

Abuses that seemed expedient–or at least comprehensible–to many in the months after 9/11 are now properly understood even by Republicans as part of the Bush Administration’s broader pattern of abuse of executive authority, visible from Iraq to Louisiana. (That’s why the nomination of Timothy Flanigan–implicated in the Iraq torture memo and the Jack Abramoff lobbying scandal–for the post of deputy attorney general was abruptly withdrawn.)

McCain and his colleagues are attempting nothing less than to extricate the government from direct complicity in crimes of war. War crimes are the deepest and darkest expression of the moral degradation now permeating the White House. The McCain amendment and the President’s threat to veto it lay out the crisis facing the White House and the Republicans: a crisis of law and legitimacy.