What the rape case fiasco and the U.S. attorney scandal have in common.

Today represents one of those serendipitous moments in which two scandals merge. Where the denouement of one national outrage—the Duke rape fiasco—reveals something incredibly important about another one—the U.S. attorney purge. Both cases highlight the stunning power of prosecutors and the need for those prosecutors to be as independent and honest as possible.

If this afternoon's statement by North Carolina Attorney General Roy Cooper—announcing that all charges had been dropped against the three former lacrosse players—clarified anything, it was that the catalyst for all of the harm in the Duke case was Durham County District Attorney Mike Nifong, whose "tragic rush to accuse and failure to verify serious allegations" has ruined lives, probably irreparably. Cooper didn't mince words today. "Rogue prosecutor" can't really be parsed in a gentle way.

That's a thought worth holding onto as we reflect on the U.S. attorney purge that's taken over the front pages of our newspapers.

It's easy to be distracted, even slightly amused, by the banal office shenanigans that make up the day-to-day coverage of the scandal. Increasingly, the Justice Department is revealed in all its wacky Dunder Mifflin glory. Alberto Gonzales is unmasked as The Office's Michael Scott—in so far over his head that he has no idea what his youthful employees are up to. With our daily focus on who was e-mailing whom and who was spending what on their fancy investitures, it's tempting to dismiss senior Justice Department staff ranking U.S. attorneys for their "loyalty" to the president as sophomoric. The Duke case is a useful reminder that the little plastic game cards being shuffled around and swapped by Kyle Sampson and Monica Goodling were, in fact, loaded weapons.

Federal prosecutors, like state district attorneys, have tremendous power and almost limitless discretion to launch investigations, to subpoena, to file charges, to question witnesses, and to drop charges when the facts don't bear them out. And if the Duke case reminds us of anything, it's that the innocent targets of such investigations and indictments have only one power: to wait it all out and hope for the best.

When politics are injected into these individual prosecutions—when officials have one eye on the law and the other on mollifying either the party bosses or local voters—it's a certainty that justice will be lost in the shuffle. Look at the list of Mike Nifong's prosecutorial errors, as cataloged today by Cooper: "The eyewitness identification procedures were faulty and unreliable"; "no DNA confirms the accuser's story"; "no other witness confirms her story"; the witness even "contradicts herself." Yet still Nifong drove forward with his case.

In Durham, the politics that drove Mike Nifong were complicated: Race and class and his need to pander to voters in an election year may have motivated him, in the words of Attorney General Cooper, to "push forward unchecked." But if these subtle pressures can twist a district attorney in Durham, imagine the damage to justice when a U.S. attorney is pressed by the White House, or his congressman, to haul in more death penalties, at whatever cost, or to hand down an indictment by November.

Senate Democrats have begun to scrutinize the prosecutions undertaken by some of the U.S. attorneys who kept their jobs last year, beginning with the case of a Wisconsin state worker who got an 18-month jail sentence for a corruption case. When a three-judge panel of the 7th Circuit Court of Appeals dramatically overturned Georgia Thompson's conviction after oral argument last week and ordered her released immediately from prison, one of the judges opined that the prosecution's evidence against her was "beyond thin."

On the basis of that thin evidence, however, Thompson served four months in prison, lost her job, and sold her home in order to pay more than $250,000 in legal bills.

Both the Duke case and the U.S. attorney purge confirm that there is no such thing as law without politics or politics without law. But both stories ought to remind us that "prosecutorial independence" isn't just some meaningless ethical jargon or a gauzy law-school ideal. Former Attorney General and Supreme Court Justice Robert H. Jackson gave a speech in 1940 in which he warned that "[t]he prosecutor has more control over life, liberty, and reputation than any other person in America. His discretion is tremendous. He can have citizens investigated and, if he is that kind of person, he can have this done to the tune of public statements and veiled or unveiled intimations." Jackson added that "the citizen's safety lies in the prosecutor who tempers zeal with human kindness, who seeks truth and not victims, who serves the law and not factional purposes. ..."

We've heard those words a lot these past weeks, but it took Mike Nifong to make them real.

Dahlia Lithwick is a Slate senior editor.