James Anderson, the Pentagon’s acting undersecretary of defense for policy, resigned Tuesday a day after President Trump fired Defense Secretary Mark Esper. Anderson had been assigned to second-in-command, but had been acting as the Pentagon’s top policy chief since June. “Now, as ever, our long-term success depends on adhering to the U.S. Constitution all public servants swear to support and defend,” Anderson wrote in his resignation letter, which came in advance of an expected request to resign from the White House.

Insiders told Politico they expect Anderson to be the first of several departures after Esper’s firing, and that he’d clashed with other Trump appointees. His departure leaves a power gap possibly to be filled by his deputy Anthony Tata, who was pulled from consideration for the top job last year over Islamophobic tweets. Tata also pushed “deep state cabal” conspiracy theories.