Chief Petty Officer Shannon Kent was killed in action during a special operations mission in Syria in 2019. Mr. Kent said he could not support “sending the next generation off to fight and die” in Iran.

As a lawsuit by the former staff drags on, the fight highlights President Trump’s upending of traditional peace-building and the lasting effects of his administration’s cost-cutting blitz.

Mr. Larijani, the top national security official and a confidant of the former supreme leader, expertly navigated Iran’s internal politics and led the brutal crackdown on protests this year.