The arrest of Illinois Governor Rod Blagojevich and his chief of staff, John Harris, may end up being one of the most serious public corruption cases prosecuted by the Justice Department in many years. The 78-page complaint and accompanying affidavit of FBI Special Agent Daniel Cain reads like something out of a Mickey Spillane novel, particularly the snippets of conversations between Blagojevich and Harris (with the Governor’s wife yelling epithets in the background) recorded on the wiretaps placed on the Governor’s telephones.

The charges of conspiracy to commit mail and wire fraud and solicitation of bribery are based on actions including the attempted selling of President-elect Obama’s Senate seat; making financial assistance to the Tribune Company from the Illinois Finance Authority conditional on the firing of editorial board members at the Chicago Tribune who had been critical of Blagojevich; and obtaining campaign contributions in exchange for official actions by the Governor. Probably the most disturbing example of Blagojevich’s alleged corruption is his alleged solicitation of a $50,000 contribution from an executive of Children’s Memorial Hospital in Chicago, and his discussion of the feasibility of rescinding $8 million in state funds received by the hospital after the contribution was not made.

Patrick J. Fitzgerald, the U.S. Attorney in Chicago, is garnering a lot of praise for his pursuit of this case. There is no question that this is the kind of public corruption and bribery that directly threatens our democratic system of government. It is also the type of public corruption that the FBI should be investigating and that the Department of Justice should be prosecuting. However, before Fitzgerald obtains too many laurels, we should all remember the previous high-profile case he prosecuted.

Fitzgerald’s persecution of Lewis “Scooter” Libby was one of the worst examples of prosecutorial overreach I have seen in Washington (and I served as a lawyer at the Department of Justice for four years). Despite knowing before he began his investigation into the Valerie Plame leak that the leaker was Richard Armitage, Fitzgerald pulled Libby in front of a federal grand jury anyway to question him about the leak. Why did Fitzgerald never indict Richard Armitage? Because the leak of Plame’s status at the CIA did not constitute a violation of the statute prohibiting disclosure of an intelligence agent’s identity. Yet Libby was indicted (and unfortunately convicted) for obstruction of justice and perjury for supposedly lying when there was no underlying crime and his conversations with Robert Novak were perfectly legal.

Being able to distinguish between the kind of serious public corruption represented by the Blagojevich case and the type of political persecution represented by the Libby case is the heart of prosecutorial discretion. It is the sign of not only a good prosecutor, but of a good public servant who can be trusted not to abuse the great power that resides in federal law enforcement agencies like the Department of Justice. In addition to their legal and ethical obligations, prosecutors have a moral obligation to distinguish between such cases to prevent the unjust operation of the law. Fitzgerald entirely failed that test in the Libby case in his misplaced zeal to obtain a conviction – let’s hope his zeal in this case will follow the evidence wherever it may lead.