For a generation after losing the Vietnam War, the American military soothed itself with a “stabbed in the back” narrative: If not for meddling politicians, intrusive journalists and a spineless public, the military would have won the war. In his book, “Dereliction of Duty,” H.R. McMaster (then a young Army major) demolished this palliative myth, carefully using historical evidence to show how military leaders failed their troops and their country by remaining silent — or worse — during the escalation in Southeast Asia. Along with other volumes focused on the conduct of the war, McMaster’s work helped reallocate blame for America’s failures in Vietnam to those in uniform who deserved their share of culpability.

In the book, McMaster carefully avoided many of the larger questions raised by his scholarship, such as whether military dissent might have altered the course of the Vietnam War — both as a matter of good historical tradecraft and career savvy. This past week, McMaster, now a three-star general and bona fide hero of the first and second wars in Iraq, was tapped by President Trump to be national security adviser. The big questions he didn’t take on in print 20 years ago now loom large for him and the White House: Can an insular and politicized team make effective national security policy? Should military officers speak up when they see policy going off track? Would it make a difference if they did? And how should civilian officials encourage dissent from the Pentagon?

“Dereliction of Duty” painstakingly dissects four major decisions between 1963 and 1965 that led the United States deeper into Vietnam. McMaster shows how military chiefs failed repeatedly to raise dissenting views about escalation, unable to penetrate the inner sanctums of the White House and meaningfully change the course of the war. In one anecdote, McMaster describes how Army Gen. Earle Wheeler told his staff that he planned to object to President Lyndon B. Johnson’s decision in 1965 to send more troops to Vietnam without calling up additional reservists. But when asked directly by Johnson whether he agreed with the move, Wheeler silently nodded and indicated his assent. Dereliction of duty, indeed.

Part of the problem lay in how both John F. Kennedy and Johnson after him relied on a small, insular, executive committee of political aides and National Security Council staffers to make decisions. This “ExComm” model worked well during the Cuban missile crisis; it broke down during the grinding years of war in Vietnam. Kennedy disdained advice from senior military leaders, in large part because of his World War II experience, as well as his initial involvement with the service chiefs during the Bay of Pigs fiasco and the missile crisis. Johnson trusted his political instincts more than the military leadership. Regardless of the cause, the effect was the same: Senior military officers were cut out of the loop.

McMaster now assumes the role played by McGeorge Bundy in his book, a different one than he has prepared for during his lifetime of military service. But much of the background is similar. Like Kennedy and Johnson, Trump has chosen to make decisions by relying on a small, insular team of political advisers. McMaster knows, even if his new colleagues don’t, that there is a better way to organize the White House and engage the brass in making national security decisions. ...