Yes, undisclosed marital infidelity can result in the loss of a security clearance, but the primary issue is often the concealment itself rather than the infidelity. The case is typically adjudicated under Adjudicative Guideline D (Sexual Behavior) and, more importantly, Guideline E (Personal Conduct). The government’s concern under Guideline D is that hidden sexual behavior can make an individual a target for blackmail or coercion by a foreign intelligence service. The secret creates a vulnerability.
The Guideline E concern is about honesty and integrity. If an applicant is asked about extramarital affairs on their SF-86 security questionnaire or during an interview and they deliberately lie or conceal the information, this is considered a serious lack of candor. The adjudicator will reason that if the applicant is willing to lie to the government about their personal life, they cannot be trusted to be honest about other security matters or to safeguard classified information. The act of falsification is often viewed as more disqualifying than the underlying affair.
A security clearance attorney defending an applicant must address both issues. They will advise the client to be completely truthful and to self-report the conduct if it was previously omitted. The attorney will then build a mitigation case. They will present evidence that the affair is over, that the vulnerability to blackmail no longer exists (e.g., the spouse is now aware), and that the applicant has taken steps to ensure responsible future conduct. The goal is to show the judge that despite the past poor judgment, the applicant is currently reliable and trustworthy.…