It remains to be seen whether the affair was the only reason for Petraeus's departure, but having an affair as a CIA director can certainly be considered a security risk worth leaving the agency over.
After getting a tip that Petraeus was involved in an affair, the FBI launched an investigation to determine whether the relationship posed a "potential security risk," CNN reported.
The official added there is no suggestion the FBI was probing Petraeus for any criminal wrongdoing, only because they feared he might be "in a vulnerable spot."
Anyone applying for a Top Secret for Sensitive Compartmentalized Information (TSSCI) clearance would be denied for simply having any outstanding debt. Something as simple as a DUI or alcohol problem can endanger passing a Secret Clearance review, which is one lower than TSSCI (also referred to as a 'need-to-know').
Had a foreign agent found out Petraeus was involved in an extramarital affair, the resulting leverage could have been astounding.
The New Yorker's Amy Davidson puts forth a flurry of possibilities as to how the affair might have compromised his own or the CIA' security:
In addition to the blackmail issue, one imagines that he will at least be asked about where he might have been with classified material ... Did he give answers in the course of security-clearance checks that turned out to be lies? Was someone trying to destroy him? Did it involve a subordinate — and what was the timing, and did it extend to his tenure as an Army general; did it involve his command?
According to Clearancejobs.com, a career site for individuals with security clearances, "Most sexual misconduct is either not a potentially disqualifying condition for a security clearance or can be fully mitigated by 'passage of time without recurrence' and the absence of any susceptibility to blackmail or coercion."
What's more, very few security clearance cases cite sexual behavior as a security threat:
Of the approximately 1160 cases decided by administrative judges at Defense Office of Hearings and Appeals (DOHA) in 2009 only 36 cited “Sexual Behavior” as a security/suitability issue. Almost all of these 36 cases involved criminal conduct, and about half involved criminal convictions for sexual offenses. Only 2 cases cited extramarital affairs, and both of these cases involved current sexual relationships about which their spouses were unaware.
Then again, most of those people weren't applying to be director of the CIA.