President Donald Trump on Monday named U.S. Army Lt. Gen. H.R. McMaster his new national security adviser.

The announcement comes a week after Michael Flynn resigned the position when he lost the trust of the administration because of his discussions with a Russian ambassador prior to Trump taking office.

McMaster is a career officer in the Army and wrote a book critical of the Vietnam War in 1997 called "Dereliction of Duty." A 2006 story from CNN labeled then-Col. McMaster as a "rising star" and called his book "the seminal work on military's responsibility during Vietnam to confront their civilian bosses when strategy was not working."