A president's ability to govern effectively depends on a measure of accountability -- the public's confidence that the leader will hold subordinates accountable for lapses in performance, ethics and judgment. That is precisely the quality that is beginning to slip away from the Bush administration, just six months into its second term.

The Bush White House's stonewalling and temporizing in the leak investigation of Karl Rove is the most dramatic sign of this problem, but it isn't the only one. This is an administration that rarely holds anyone accountable for anything, other than political disloyalty. That has been the problem on Iraq and Abu Ghraib. People who make mistakes, or worse, have had too many medals pinned on them.

President Bush tried to evade this leadership problem Monday when he adjusted his defensive perimeter in the Rove investigation. "If someone committed a crime, they will no longer work in my administration," the president said. That may be the right course legally -- there's a lot we still don't know about the investigation by special counsel Patrick Fitzgerald, and history certainly offers many examples of grand jury investigations of prominent figures that turned out to be witch hunts.

But Bush's stance doesn't work politically. Look at the polls and you can see that the administration is losing public confidence. An ABC News poll released Monday showed that just 25 percent of the public believes the White House is cooperating fully with Fitzgerald's probe, compared with 47 percent when the investigation began in September 2003. Most striking in the ABC poll was the unanimity of opinion across party lines. Asked if Karl Rove should be fired if he leaked classified information, 71 percent of Republicans said yes. That was just a few points lower than the 75 percent average for all voters.

In place of accountability, the Bush White House has embraced the three-pronged strategy of attack, attack, attack. If anyone had forgotten how these trash-the-enemy rules operate, Republican National Committee Chairman Ken Mehlman gave an astonishing demonstration on Sunday's talk shows. Mehlman had a tough case to argue, given uncontroverted evidence that (a) Rove had been a confirming source for columnist Robert D. Novak's initial story that the man who was making trouble for the White House on its arguments regarding weapons of mass destruction, Joseph Wilson, was married to a CIA employee and (b) Rove was the initial source for Time's Matthew Cooper on information that Wilson's wife worked at the CIA on WMD issues.

Mehlman didn't bother to defend the indefensible. He attacked. "Democrat partisans on the Hill have engaged in a smear campaign where they have attacked Karl Rove on the basis of information which actually vindicates and exonerates him, not implicates him." Now, I'm sorry, but that's about as close to the Big Lie as we get in American politics. It's like claiming that the blue sky overhead is actually some other color -- and then challenging the dissenter to prove it's blue. Mehlman's comments have the effect of undermining the shared ground on which government operates.

Partisan attacks have worked pretty well for the Bush White House, but it may now be pulling too hard on the string. Take a close look at other polls and you'll see an increasingly mistrustful public. A mid-July poll by the Associated Press showed disapproval of Bush's job performance at 56 percent, the highest level ever. A June poll by CBS News and the New York Times found that only 35 percent of the public said Bush had the same priorities for the country that they did.

The poignancy of this drama is that you can see the administration's weaknesses slowly leaching away its strengths. In Rove's famous June 22 speech to the New York Conservative Party, he evoked the qualities the administration wants to be remembered for. "We are seizing the mantle of idealism," Rove said, referring to the president's campaign for democracy in Iraq and the Middle East. Conservatives are "agents of reform," he said, referring to Bush's drive to restructure Social Security. But what made headlines was Rove's outrageous claim that after Sept. 11 liberals wanted to "offer therapy and understanding for our attackers." What made his comment truly reckless was that it ripped at the cohesion America needs in wartime.

Presidential second terms are slippery slopes. People get arrogant; they start to think that because they won reelection, the political rules of gravity no longer apply. Presidents Ronald Reagan and Bill Clinton were brought crashing back to earth by bad mistakes in their second terms. This summer we are watching another reminder that reelection doesn't suspend the laws of accountability.

davidignatius@washpost.com