His approval rating has cratered. His legislative agenda, after the collapse of immigration reform, is in ruins. So many longtime aides have departed that he may need name tags for Oval Office meetings. And yet with his decision to spare I. Lewis Libby from prison, President Bush sent his critics a clear signal that he will not concede an inch of ground that they lack the strength and determination to take from him.

Commuting Libby's sentence fits within a flurry of administration decisions that confront the president's opponents. Bush is defying subpoenas for documents and testimony from the House and Senate Judiciary committees. He's drawn a line in the sand (box) against Democratic proposals to provide health insurance for millions more children in working-poor families. His vice president recently claimed to have discovered a previously uncharted fourth branch of government with himself as the sole known resident.

Immigration, on which Bush worked across party lines, was the exception to this pattern. But the dominant message of his recent maneuvers is that even at low ebb, Bush hasn't abandoned his pugnacious approach to governing. If he can implement his ideas, he does, regardless of whether he's built consensus for them. Bush rarely changes course unless his critics prove they can block his initial preference. That was the case again with his decision to erase Libby's prison sentence. Bush could not have doubted the uproar he would provoke from Democrats by protecting from prison a convicted felon who undoubtedly possessed the ability to embarrass the administration. Yet because his opponents couldn't stop him, Bush stood in the jailhouse door.

That example has the most relevance for the congressional debate about Iraq, which will resume next week with new Democratic challenges to Bush's policy. The Libby decision's clear implication is that unless opponents can make it politically unsustainable for Bush to maintain his current direction in Iraq, he's likely to resist anything beyond cosmetic change — no matter how much his support in Congress and the rest of the United States erodes.

No one in Congress needs to consider that message more than the Republicans uneasy with Bush's Iraq strategy but unwilling to break with him over it. Chief among those is Sen. Richard G. Lugar, the thoughtful but deferential Indiana Republican who was chairman of the Senate Foreign Relations Committee during most of Bush's presidency.

In a compelling speech last week, Lugar summarized the case against Bush's Iraq policy with an airtight finality that Clarence Darrow might have envied. Even if Bush's "surge" in U.S. troops reduces violence on the ground, Lugar argued, it could not fulfill the mission of promoting reconciliation among Iraq's warring factions, because those factions do not want to reconcile. And even if national leaders somehow settled their differences, he warned, they lack the authority to impose any such settlement on their local followers, who fight under the lash of their own furies.

Nor, Lugar insisted, could the United States much longer maintain such an elevated presence in Iraq without unacceptably damaging military readiness — and provoking unacceptable levels of political conflict at home. The better course, he insisted, was to start withdrawing American troops, shift the focus for those who remain from combat to training and launch a diplomatic offensive on all of the Middle East's intertwined problems.

But in subsequent interviews, Lugar indicated that despite his rejection of Bush's policy, he will not support legislation to change it. Instead, he said, Congress should avoid direct confrontations with the president, while trying to persuade him to reassess.

With that conclusion, Lugar echoed the flawed logic he applied as Foreign Relations chairman from 2003 through 2006. On Iraq, Lugar minimized public confrontations with the administration to maximize his private access to it. He retained a more critical perspective on the war than most Senate Republicans, but his committee too often stood silent as Iraq disintegrated into chaos.

Lugar risks compounding that mistake. Like other uneasy Republicans, he hopes to persuade Bush to change course in Iraq. But Lugar might have as much luck persuading a boulder to stop rolling downhill.

The lesson of Libby is that consensus matters no more to Bush today than when he was at his apex. He responds to power, not argument. Watching Bush shrug off the Democratic outrage over Libby ought to show Lugar and other uneasy Republicans how much their softer words on Iraq will affect the president — unless they command his attention with a sharp slap of repudiation in the votes on the war that will soon consume Congress again.

Ronald Brownstein is the Los Angeles Times' national-affairs columnist.