So now we know what we’ve pretty much known all along about the CIA-leak case: The leaker was Richard Armitage. A new book by Michael Isikoff and David Corn, Hubris: the Inside Story of Spin, Scandal, and the Selling of the Iraq War, reports that it was Armitage, the former number-two at the State Department and a confidant of former secretary of state Colin Powell, who told columnist Robert Novak about Valerie Plame — thus setting off the CIA leak “scandal” and a years-long investigation.

This revelation lays waste to the notion that Vice President Dick Cheney, former Cheney chief of staff Lewis Libby, and top White House aide Karl Rove conspired to “out” Plame as a way of smearing her husband, the anti-Bush gadfly Joseph Wilson. But it does more than just debunk left-wing conspiracy theories. It also raises a vitally serious question about the CIA leak investigation itself: Why did it happen?

Nobody much noticed back on July 14, 2003, when Novak reported that Plame, a CIA employee, had had a role in sending her husband to Niger to check out claims that Saddam Hussein was seeking WMD components there. But that changed a few days later when David Corn (the left-wing co-author of the just-released Hubris), relying on Wilson as a source, became the first person to publish a story explicitly raising the possibility that Plame was an undercover CIA operative, and that the exposure of her identity was a crime. “The Wilson smear was a thuggish act,” Corn cried.

His version of events, apparently based entirely on Wilson’s self-serving statements, was quickly picked up by New York Democratic senator Charles Schumer, who demanded an investigation. CIA director George Tenet then sent a letter to the Justice Department requesting a probe. It was conveniently leaked to the press, which amplified the demand and put enormous political pressure on the administration.

So in October 2003 the investigation began. FBI agents quickly talked to Armitage, Rove, and others. And guess what? Armitage told the FBI that he was Novak’s source. And Rove told the FBI that he was Novak’s secondary source (that is, he had confirmed what Novak had already learned from Armitage). Within days of beginning the investigation, the Justice Department had answered the question that started it.

Things should have stopped right there. FBI investigators knew who the leakers were; they knew that no one had violated the Intelligence Identities Protection Act or any other national-security law; and they knew there had been no White House conspiracy to attack a critic. Yet then–attorney general John Ashcroft, apparently afraid of the political repercussions of doing the right thing, allowed the investigation to go forward. He recused himself and handed the case over to top Justice Department official James Comey, who then also bowed to political pressure and appointed his friend Patrick Fitzgerald — already busy with his job as the U.S. attorney in Chicago — to head the probe.

Since then, Fitzgerald has called Rove and dozens of others to testify before a grand jury, and has set an awful precedent by finding novel ways to force reporters to reveal their sources in court. And all for what? One indictment, of former Cheney aide Lewis Libby — and not for any crime related to the leak, but on charges of perjury and obstruction of justice in the subsequent investigation. That isn’t to minimize those crimes if they were committed (the case against Libby looks rather less than airtight), but to emphasize that there was no need for the investigation in the first place.

Today, nearly three years on, we are basically right where we started. There’s a lot of blame to go around. First up is Armitage. There was absolutely nothing illegal about the original leak he committed, but he chose to remain silent while others — principally Rove and Libby — endured years of accusations in the press. (Armitage’s close friend Colin Powell also deserves a dishonorable mention for keeping quiet after learning of Armitage’s role.) The administration’s leftist adversaries in and out of government who have spent years shrieking “traitor” should be ashamed of themselves. Likewise the New York Times editorial board, which screamed for an investigation until it got bit it on the backside in the form of the media subpoenas. Fitzgerald should ask himself whether his wild goose chase has shown the judgment and discretion one expects from such an experienced prosecutor. Finally, the higher-ups at the Justice Department — Ashcroft and Comey in particular — bear great responsibility for buckling under political pressure when their own investigators knew there was nothing to the story.

It’s a sorry mess. And yet the investigation continues. If common sense suddenly prevailed — a remote possibility, we concede — it would be shut down. Now.