IN AMERICA'S presidential system, calls for the resignation of top politicians are rare. Even during that most shameful of episodes, the Lewinsky affair, comparatively few politicians echoed The Economist's cry that Bill Clinton should go. So when members of Congress demand the resignation of the attorney-general, Janet Reno, three times on three different charges in two years—most recently the new revelations about the siege at Waco, Texas, in 1993—it is clear that something is rotten in the Justice Department.

Is it just Ms Reno herself? Conservatives would say so. The longest serving attorney-general since the days of John Quincy Adams, she has had more than her fair share of misjudgments. She came to Washington in 1993 as a little-known state attorney from Florida, with a reputation for running an enlightened and effective anti-drug policy but no political backing in Congress or even in the White House. She won a good deal of public credit for her willingness, in April 1993, to be held accountable for the disastrous operation at Waco. Much of this has disappeared with her claims, in the past few weeks, that she knew neither exactly what the FBI was doing at Waco nor how flagrantly it lied about it afterwards.

On other matters, the accusations against her are less clear-cut. She was asked by the FBI to authorise a wire tap on Wen Ho Lee, a scientist at the centre of Chinese spying allegations. She refused. She refused again when Republicans asked her to appoint an independent counsel to investigate allegations of campaign-finance abuses by both President Clinton and Vice-President Al Gore. On both occasions, her actions, though controversial, were legally defensible. She demanded more prima facie evidence of wrongdoing than her critics thought necessary.

Such conflicts suggest there is more to Ms Reno's troubles than personal error. In both cases, her legal judgment collided with political opinion and failed to satisfy it. That tension between the law and politics is intrinsic to her job. But recently public and congressional demands upon her have risen so much that it is becoming harder and harder for Ms Reno—or anyone else—to satisfy both parts of the attorney-general's brief.

The 1789 Judiciary Act requires the president to appoint a person “learned in the law” to advise him on legal matters. Like any lawyer, therefore, the attorney-general must serve two masters—the president and the law. When the two come into conflict, the only way to resolve it is for the attorney-general to leave office and trust to the public to force the president to obey the law. That is exactly what happened in the “Saturday night massacre” of 1973, when Richard Nixon kept on firing attorneys-general until he found one willing to get rid of the Justice Department prosecutor who was investigating the Watergate affair. Ms Reno, in other words, is not the first to run into this dilemma.

She is unusual in the number and complexity of the conflicts that beset her. But there is an institutional as well as a personal explanation for that. For many years, the tension inherent in her post was muted because few people thought it was the main job of the attorney-general to investigate the government. John Kennedy even appointed his brother as attorney-general. Watergate changed both the attorney-general's job and the way it was perceived by the public—in diametrically opposing ways.

The scandal led Congress to pass the independent counsel law. This said that, when any of 49 top officials was alleged to have committed a crime, the attorney-general could name an independent counsel to investigate. In practice, this meant setting up miniature departments of justice, independent of the attorney-general, whenever there was a problem. The law lapsed in July—but not before it had done much to erode the attorney-general's power and accountability.

Watergate also led to the establishment of inspectors-general in federal agencies to audit and investigate them. The inspectors report to Congress, which means that they too serve two masters while simultaneously competing with the attorney-general.

Yet, at the same time, Watergate gave the public a sense that the attorney-general ought to have more political independence. Ms Reno herself is a perfect expression of that expectation. She has been almost ostentatiously independent of the president, but her greater independence is a matter of public attitude only. There is no constitutional or legal mandate for it.

The weaknesses of this arrangement—the attorney-general is expected to do more but has fewer powers—have been ruthlessly exposed by the so-called “criminalisation of politics”. This does not refer to any increase in the tendency of criminals to become politicians, or vice versa. It refers to the recent practice of using allegations of wrongdoing as weapons in what are political, not legal, battles. This week, Henry Cisneros pleaded guilty to charges of not telling the FBI how much he was paying his admitted mistress before he became Mr Clinton's first housing secretary. No one has pretended that his affair had any relevance to his ability to do his job. There have been dozens of other such investigations, most notably Kenneth Starr's. Few have discovered irrefutable cases of corruption or illegality.

Ms Reno is the central figure in this pursuit of politics by other means. Her department must investigate the allegations or recommend a special prosecutor (it seems about to choose a respected former Republican senator, John Danforth, to look into Waco). Her personal integrity has made her all the more willing to appoint special prosecutors (when she was a lawyer in Miami, she called in a special prosecutor to investigate drunk-driving charges against her own mother). But because the arguments are at root political ones, legal processes can never resolve them fully.

This is a far cry from the usual charge against Ms Reno: that she has abused her office to protect the president. Of that, she is almost certainly innocent. She may have been guilty of bad management in the Waco operation: Mr Danforth's investigation should settle that. But what is certain is that she has been unable to stop something much more corrosive: the use of her office by others to fight their political battles.