Brendan Smialowski / Getty Images President Barack Obama listens while then-nominee for CIA Director, Gen. David Petraeus, speaks in the East Room of the White House in Washington, April 28, 2011.

Forget the salacious details of David Petraeus‘s affair with Paula Broadwell for a moment. Focus on the key national security facts: the head of the CIA was having an extramarital affair, and was communicating with his mistress over an unsecure Gmail account for up to eight months. In the world of espionage, those are potentially important—even vital—secrets, and certainly ones that the Commander in Chief should know. The affair could expose the CIA chief or the mistress to blackmail. The use of an unclassified e-mail account to communicate potentially damaging details of his private life could speak to the judgment of the nation’s top spy.

For these reasons, an official who knew those secrets and didn’t tell the President had better have a good reason for keeping them to himself. And yet the Obama Administration has offered little explanation as to why the Justice Department kept the the President in the dark about the Petraeus affair until two days after the election. Prosecutors and FBI agents knew at least as early as last July that the affair was occurring; high-level Justice officials, including Attorney General Eric Holder, knew in “late summer.” According to White House Press Secretary Jay Carney, the President “was obviously surprised” when he learned of the affair on Nov. 8.

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At a press conference Tuesday, Carney brandished the word “protocol” seven times. “There are protocols that the FBI follows with regards to these kinds of notifications,” he said. Administration officials speaking on background are a little more specific. A law enforcement official told TIME Tuesday that the investigation “was handled as routine criminal investigations and ongoing criminal investigations are handled.” Why wasn’t the President told? “Allegations get bandied about,” the official says. “So until you run those down you don’t share them outside of law enforcement. That’s one reason. Another reason — probably a more compelling reason — is criminal investigations can result in criminal charges. You don’t talk about evidence or things that might be crucial to a prosecution outside of the law enforcement agency, because you could potentially jeopardize the potential prosecution.”

Such prudence is a well-established approach, the law enforcement official says. “This has been long standing practice for many, many years.” The official cited a 2007 memo by then Attorney General Michael Mukasey regarding contacts with the White House during criminal investigations. As part of the process of cleaning up the politically motivated firing of U.S. Attorneys under his predecessor, Alberto Gonzales, Mukasey issued explicit instructions that Justice officials had to follow. “Alerting the White House of an ongoing investigation? That’s a huge no-no,” the law enforcement official says.

Unfortunately for the Obama team, there are huge holes in their arguments. For starters, Mukasey himself says there is no prohibition on Justice-to-White House communication in criminal investigations. “The memo makes it quite clear that not only is that not the case, it is explicitly not the case,” Mukasey told TIME Tuesday evening. Says Mukasey: “The point is not that the White House can never be apprised of a pending criminal investigation; the point is that the White House should not reach out and influence a pending criminal investigation.”

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More to the point, Mukasey’s memo specifically instructs “all components of the Justice Department” that “it is critically important to have frequent and expeditious communications relating to national security matters, including counter-terrorism and counter-espionage issues.” If anything, the Mukasey memo orders Justice Department officials–including prosecutors and the FBI–to communicate with relevant political authorities when they make a discovery like they did in the Petraeus case.

The Mukasey memo isn’t binding on the current Attorney General, or the Justice Department. But it is not the only precedent that suggests the Administration handled the Petraeus affair badly. In late 1996, the CIA began an investigation of then Director John Deutch after computer security experts found classified information on his unclassified home computer, including details of some of the agency’s most closely held covert operations. His successor George Tenet was widely criticized for not informing the Justice Department about the security breach, and belatedly suspended Deutch’s security clearance.

Administration officials declined to provide any further specific protocols that prevented them telling the President about Petraeus’ affair. Instead, the Administration is trying to stretch the facts of the Petraeus case to fit the Mukasey memo and other precedents. On one hand, they argue that national security was never an issue. “Early enough on in the investigation, any national security threat was ruled out,” says the law enforcement official. On the other hand, they argue that they can’t risk telling anyone outside Justice, because Petraeus might become a target. “You don’t know where the facts are going to go. What if he becomes [a target?]” says the official.

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Why criminal evidence might turn up but national security evidence wouldn’t is anyone’s guess. For his part, Mukasey argues it is obvious that an ongoing extramarital affair by the CIA chief is a potential national security issue. “They know enough at the point that his name turns up,” says Mukasey. “He’s doing it on a Gmail account which any intelligence agency in the world would want to know about, and if they did know about, would feel in a position to use.”

The only remaining question is how President Obama feels about his Attorney General keeping him in the dark for so long. Presumably we’ll get that answer later today at his press conference.

Here’s the “decretal,” or tasking, part of the Mukasey memo:

“…All components of the Department, including federal law enforcement agencies and the United States’ Attorneys’ Offices shall abide by the following limitations: “With the exception of national security related matters, which are discussed below, all initial communications between the White House staff and the Justice Department regarding any specific pending Department investigation or criminal or civil-enforcement matter should involve only the Counsel to the President or Deputy Counsel to the President and the Attorney General or Deputy Attorney General. Initial communications regarding civil-enforcement matters may also involve the Associate Attorney General. Initial communications regarding a matter on appeal may also involve the Solicitor General. “To the extent subsequent contact is required or necessary, the Attorney General, Deputy Attorney General, Associate Attorney General, or Solicitor General may designate others within the Department to communicate with the White House staff. In all such circumstances, this designation will be limited to the fewest number of people practicable. “It is critically important to have frequent and expeditious communications relating to national security matters, including counter-terrorism and counter-espionage issues. Since September 2001, departments within the Executive Branch have made substantial efforts to remove barriers to information sharing and communication. Communications that relate to a national security matter and concern a litigation issue for a specific, pending case are not subject to the limitations delineated above so as not to reestablish those barriers or limit necessary communication. Nevertheless, such communications must be made known to the Office of the Attorney General, the Office of the Deputy Attorney General or the Office of the Associate Attorney General so that senior officials can monitor the communications and consider whether any additional limitations or safeguards are necessary.”

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