The feud between former President Trump and the nation’s highest-ranking military officer, Gen. Mark Milley, played a key role in the historic indictment handed down last week over Trump’s alleged criminal mishandling of classified documents.

Key audio in the case captured Trump trying to prove his side of the story after a New Yorker article detailed Milley’s attempts to prevent the president from attacking Iran during his final days in the White House.

Trump claimed he had a document about a “plan of attack” on Iran that showed it was Milley’s idea, and he admitted he knew the document was secret and not declassified by him, contradicting some of his claims in the case. It’s unclear whether the document in question exists.

The episode highlights a tumultuous relationship that began when the former president tapped Milley as the Joint Chiefs chairman in late 2018. 

The public feud has largely been in one direction, with Trump fuming at Milley since leaving office. But while Milley has yet to publicly hit back against the former president, he has acknowledged regularly speaking on background with reporters. 

While Trump clashed with a number of his cabinet members and aides, the disagreements with Milley likely hurt more because of the military’s public prestige, said Peter Feaver, a professor of political science at Duke University focused on the military.