The claim was made during oral arguments in an appeal filed by Nathan Michael Smith, a now-former Army intelligence analyst who sued last year claiming former President Barack Obama was illegally fighting Islamic State terrorists without an authorization for use of military force, or AUMF, from Congress.

Smith, who left active-duty military service in June, supports fighting the jihadi group, but argues doing so has not been properly authorized by Congress. "For me, it's not a partisan issue," he told the Washington Examiner outside a courtroom in the nation's capital. "Procedure matters, if we're a nation of laws."

Judges considered various arguments that Smith's case should be thrown out, including that he has no standing to sue — a matter focused on whether a coerced choice between violating his oath of office or risking court martial is sufficient.