"What did the president know and when did he know it?" a Republican senator — Howard Baker of Tennessee — famously asked of Nixon 30 springtimes ago.

Today, confronted by the graphic horrors of Abu Ghraib prison, by ginned-up intelligence to justify war, by 652 American deaths since presidential operatives declared "Mission Accomplished," Republican leaders have yet to suggest that George W. Bush be held responsible for the disaster in Iraq and that perhaps he, not just Defense Secretary Donald Rumsfeld, is ill-suited for his job.

Having read the report of Major Gen. Antonio Taguba, I expect Baker's question will resound again in another congressional investigation. The equally relevant question is whether Republicans will, Pavlov-like, continue to defend their president with ideological and partisan reflex, or remember the example of principled predecessors who pursued truth at another dark moment.

Today, the issue may not be high crimes and misdemeanors, but rather Bush's failure, or inability, to lead competently and honestly.

"You are courageously leading our nation in the war against terror," Bush told Rumsfeld in a Wizard-of-Oz moment May 10, as Vice President Cheney, Secretary of State Colin Powell and senior generals looked on. "You are a strong secretary of Defense, and our nation owes you a debt of gratitude." The scene recalled another Oz moment: Nixon praising his enablers, Bob Haldeman and John Ehrlichman, as "two of the finest public servants I've ever known."

Sidestepping the Constitution

Like Nixon, this president decided the Constitution could be bent on his watch. Terrorism justified it, and Rumsfeld's Pentagon promoted policies making inevitable what happened at Abu Ghraib — and Guantanamo Bay, Cuba. The legal justification for ignoring the Geneva Conventions regarding humane treatment of prisoners was enunciated in a memo to Bush, dated Jan. 25, 2002, from the White House counsel.

"As you have said, the war against terrorism is a new kind of war," Alberto Gonzales wrote Bush. "In my judgment, this new paradigm renders obsolete Geneva's strict limitations on questioning of enemy prisoners and renders quaint some of its provisions." Quaint.

Since January, Bush and Rumsfeld have been aware of credible complaints of systematic torture. In March, Taguba's report reached Rumsfeld. Yet neither Bush nor his Defense secretary expressed concern publicly or leveled with Congress until photographic evidence of an American Gulag, possessed for months by the administration, was broadcast to the world.

Rumsfeld then explained, "You read it, as I say, it's one thing. You see these photographs and it's just unbelievable. ... It wasn't three-dimensional. It wasn't video. It wasn't color. It was quite a different thing." But the report also described atrocities never photographed or taped that were, often, even worse than the pictures — just as Nixon's actions were frequently far worse than his tapes recorded.

It was Barry Goldwater, the revered conservative, who convinced Nixon that he must resign or face certain conviction by the Senate — and perhaps jail. Goldwater delivered his message in person, at the White House, accompanied by Republican congressional leaders.

Republicans on the House Judiciary Committee likewise put principle above party to cast votes for articles of impeachment. On the eve of his mission, Goldwater told his wife that it might cost him his Senate seat on Election Day. Instead, the courage of Republicans willing to dissociate their party from Nixon helped Ronald Reagan win the presidency six years later, unencumbered by Watergate.

Another precedent is apt: In 1968, a few Democratic senators — J. William Fulbright, Eugene McCarthy, George McGovern and Robert F. Kennedy — challenged their party's torpor and insisted that President Lyndon Johnson be held accountable for his disastrous and disingenuous conduct of the Vietnam War, adding weight to public pressure, which, eventually, forced Johnson not to seek re-election.

Today, the United States is confronted by another ill-considered war, conceived in ideological zeal and pursued with contempt for truth, disregard of history and an arrogant assertion of American power that has stunned and alienated much of the world, including traditional allies. At a juncture in history when the United States needed a president to intelligently and forcefully lead a real international campaign against terrorism and its causes, Bush decided instead to unilaterally declare war on a totalitarian state that never represented a terrorist threat; to claim exemption from international law regarding the treatment of prisoners; to suspend constitutional guarantees even to non-combatants at home and abroad; and to ignore sound military advice from the only member of his Cabinet — Powell — with the most requisite experience. Instead of using America's moral authority to lead a great global cause, Bush squandered it.

In Republican cloakrooms, as in the Oval Office, response to catastrophe these days is more concerned with politics and PR than principle. Said Tom DeLay, House majority leader: "A full-fledged congressional investigation — that's like saying we need an investigation every time there's police brutality on the street."

When politics topples principles

To curtail any hint of dissension in the ranks, Bush scheduled a "pep rally" with congressional Republicans — speaking 35 minutes, after which, characteristically, he took no questions and lawmakers dutifully circled the wagons.

What did George W. Bush know and when did he know it? Another wartime president, Harry Truman, observed that the buck stops at the president's desk, not the Pentagon.

But among Republicans today, there seems to be scant interest in asking tough questions — or honoring the example of courageous leaders of Congress who, not long ago, stepped forward, setting principle before party, to hold accountable presidents who put their country in peril.

Carl Bernstein's most recent book is a biography of John Paul II, His Holiness. He is co-author, with Bob Woodward, of All the President's Men and The Final Days.