John Feely, the U.S. ambassador to Panama, has told Reuters that he felt “honor bound to resign” as of March 9 because he felt he could no longer serve President Trump.

Before joining the Foreign Service, he had been a Marine helicopter pilot.

“As a junior foreign service officer, I signed an oath to serve faithfully the president and his administration in an apolitical fashion, even when I might not agree with certain policies,” Feeley said, according to an excerpt of a resignation letter read to Reuters on Friday.

“My instructors made clear that if I believed I could not do that, I would be honor bound to resign. That time has come.”

“If the ambassador feels that he can no longer serve ... then he has made the right decision for himself and we respect that,” said Under Secretary of State Steve Goldstein.