The resignation of the White House press secretary, Scott McClellan, is an event of almost complete insignificance except insofar as the beleaguered White House presents it as an important change. Meanwhile, the secretary of defence, Donald Rumsfeld, under siege from dissenting ex-generals demanding his firing for arrogant incompetence, stays.

McClellan is a flea on the windshield of history. On the podium, he performed his duty as a slow-flying object swatted by a frustrated and flustered press corps. Inexpressive, occasionally inarticulate and displaying a limited vocabulary, his virtue was his unwavering discipline in sticking to his uninformative talking points, fending off pesky reporters, and defending the president and all the president's men to the last full measure of his devotion. Inside the Bush White House, he was a non-player, a factotum, the instrument of Karl Rove, Bush's chief political strategist and deputy chief of staff. McClellan played no part in the inner councils of state. He was the blank wall erected in front of the press to obstruct them from seeing what was on the other side. McClellan's stoic façade was unmatched by a stoic interior. He was a vessel for his masters, did whatever he was told, put out disinformation without objection, and was willing to defend any travesty. He is the ultimate dispensable man.

Events that could truly shake the Bush White House to its foundation, however, may be discerned elsewhere. On Monday, in Chicago, a jury found former Republican governor George Ryan guilty of 18 counts of corruption. His trial was the climax of a nine-year investigation that had yielded 75 convictions, including some of the most powerful figures in the Republican party of Illinois. The federal investigation, dubbed Operation Safe Roads, began by looking into bribery for driver's licenses. Over time, prosecutors systematically uncovered broader and deeper patterns of corruption reaching up to the governor's office. Patiently, they built their cases until they reached the top.

The United States attorney for the Northern District of Illinois, who conducted this painstakingly thorough prosecution, Patrick Fitzgerald, is also the special prosecutor in charge of the investigation into the leaking of the identity of the covert CIA operative, Valerie Plame Wilson. So far, he has indicted I. Irving "Scooter" Libby, Vice President Dick Cheney's chief of staff, on five counts of perjury and obstruction of justice.

Two weeks ago, Fitzgerald filed a motion before the federal court in the Libby case stating that his investigation had proved that the White House engaged in "concerted action" from "a plan to discredit, punish or seek revenge against" former ambassador Joseph Wilson, who revealed that the rationale of the Iraq war was based on false information that the White House knew was bogus. Fitzgerald declared further that he had gathered "evidence that multiple officials in the White House" had outed his wife's clandestine identity to reporters as an element of revenge.

Last week, on April 12, Libby counter-filed to demand extensive documents in the possession of the prosecutor. His filing, written by his lawyers, reveals that he intends to put Karl Rove on the stand as a witness to question him about his leaking of Plame's name to reporters and presumably his role in the "concerted action" against Wilson. In his request for documents from Rove's files, Libby dropped mention of Rove's current legal status.

For months, Rove's attorney, Robert Luskin, has assured the press that his client, who was believed to be vulnerable to indictment for perjury, is in the clear. But Libby insisted that he was entitled to "disclosure of such documents" in Rove's files "even if Mr. Rove remains a subject of a continuing grand jury investigation".

In white-collar criminal investigations, individuals who fall under the gaze of a prosecutor fit into one of three categories: witness, subject or target. Rove's attorney has suggested that Rove is simply a witness. But that is untrue. He is a subject. A subject is someone the prosecutor believes may have committed a crime and is under investigation. If the prosecutor decides he has accumulated sufficient evidence to prove guilt, he will change the designation of that person from subject to target and then indict him or her.

Having successfully completed his most extensive investigation and prosecution, ending with the conviction of former Governor Ryan, Patrick Fitzgerald returns to the unresolved case before him. The federal grand jury considering his evidence began meeting again this morning. Karl Rove remains a subject--for now.