Former CIA Director David Petraeus speaks at the University of Southern California in Los Angeles. Thomson Reuters In March 2015, David Petraeus, a retired general, one-time director of the CIA, and former US commander in Iraq and Afghanistan, pleaded guilty to a single misdemeanor charge of mishandling classified information.

According to The Washington Post, Petraeus had given handwritten notebooks containing "code words for secret intelligence programs, the identities of covert officers, war strategy and deliberative discussions with the National Security Council" to his biographer Paula Broadwell — who was also his mistress.

Because of Petraeus' position as one of the country's most important intelligence officials, the sensitivity of the information he gave Broadwell, and the fact that he apparently lied to FBI investigators about giving Broadwell any classified information whatsoever, many believed that Petraeus deserved something more than the $100,000 fine and two years of probation he eventually received.

A Washington Post investigation published on January 25 reveals why the renowned ex-general got off so easy.

According to The Post, prosecutors determined that Petraeus' case would simply be too difficult to prosecute in open court.

Petraeus' legal team played hardball over a potential plea deal, with the retired general refusing to plead guilty to any felonies and effectively daring the government to take the case to trial.

The strategy paid off: The one-time face of US counterinsurgency doctrine was initially facing felony charges of lying to the FBI along with "'gathering, transmitting or losing defense information' under the Espionage Act," either of which could have landed him in prison for years.

US President Barack Obama announces that Gen. David Petraeus, right, would replace Gen. Stanley McChrystal as his top commander in Afghanistan in the Rose Garden of the White House in Washington, June 23, 2010. Larry Downing/Reuters As The Post reports, Petraeus' case had a number of challenging aspects for prosecutors.

Despite her sexual relationship with Petraeus, Broadwell was protected from prosecution by her status as a biographer and credentialed journalist.

Petraeus did not intend for the information he gave Broadwell to spread beyond her or to be made public, and he personally vetted Broadwell's book for any classified information.

The Post notes that "Justice Department guidelines" hold that "it is not policy to charge [for lying to federal agents] 'in situations in which a suspect, during an investigation, merely denies guilt in response to questioning by the government.'”

Factor in his status as a major public figure, the classified nature of the case's core evidence, and its connection to the secretive upper strata of the US intelligence community, and it's unclear whether a prosecution of Petraeus would have been worth the effort, or even successful at all.

As former US attorney general Eric Holder put it in 2015, “There were some unique things that existed in that case that would have made the prosecution at the felony level and a conviction at the felony level very, very, very problematic,” according to The Post.

At the same time, intent doesn't necessarily matter in cases involving mishandled classified information.

And even if Petraeus only intended for the information he gave Broadwell to be put toward her own personal use, that doesn't mean that information was necessarily safe with her.

Paula Broadwell, the woman whose affair with CIA Director General David Petraeus led to his resignation, is seen at her brother's home in Washington, November 13, 2012. Reuters As someone in a sexual relationship with the CIA director, Broadwell was arguably uniquely vulnerable to exploitation or blackmail by a hostile intelligence agency.

It isn't surprising that The Post found law-enforcement officials who believe that Petraeus was treated too leniently.

As The Post reports, the case's outcome "left some in the Justice Department angry, particularly at the FBI, and some agents have argued privately that it will damage future efforts to secure prison terms in leak cases."

All of this might end up being good news for Hilary Clinton.

Over the past week, reports have emerged that emails on Clinton's private server, which is the subject of an ongoing FBI investigation, included information related to Special Access Programs, referring to a level of classification above top secret that is sometimes used for active intelligence operations.

Former Secretary of State Hillary Clinton. REUTERS/Faith Ninivaggi On January 24, it was reported that the FBI was looking into whether Clinton's staffers had copied and pasted classified information from the State Department's classified computer system so that they could be sent to Clinton over unsecured email.

It's technically illegal to move classified information off of a compartmentalized network, something that prohibits even a single instance of conveying classified information across an unclassified network, even if that information hasn't been explicitly marked as classified.

But The Post's report is a reminder of how difficult it is to prosecute classification-related infractions when figures at the top of the US's national-security and foreign-policy hierarchy are involved.

The government was bearish about its chances of convicting a CIA director who had knowingly given highly sensitive classified information to his mistress. The challenges of convicting a former secretary of state and a major party presidential front-runner in an election year — and in a case where any alleged intelligence disclosures didn't involve nearly the same degree of premeditation as in Petraeus' case — are probably much steeper.