President Trump shakes hands with his new national security adviser Army Lt. Gen. H.R. McMaster after announcing his appointment on Monday at Mar-a-Lago estate in Palm Beach, Fla. (Kevin Lamarque/Reuters)

After his national security adviser was forced to resign and the leading contender for his replacement withdrew, President Trump named Army Lt. Gen. H.R. McMaster to the post on Monday. The decision was quickly hailed by many within the foreign policy establishment.

Why was McMaster so widely embraced? As President Trump may soon learn, it’s because the famed soldier’s views of the world differ significantly from those of his commander in chief — including on such important issues as Russia, alliances and terrorism.

McMaster’s background is formidable

H.R. McMaster has had a storied Army career. A graduate of the U.S. Military Academy at West Point, in 1991, McMaster was a tank commander at the famed Battle of 73 Easting in Operation Desert Storm. In 2004, he oversaw the securing of Iraq’s Tal Afar. Many of his counterinsurgency tactics were later included in the Army Counterinsurgency Field Manual.

He has also been influential as part of the military’s brain trust. With an American history PhD from the University of North Carolina, he wrote “Dereliction of Duty,” a popular book examining why the United States lost its war in Vietnam. McMaster’s outspokenness probably cost him promotions at several points in his career — but also gives us insight into his worldview.

President Trump named Lt. Gen. H.R. McMaster as his new national security adviser on Feb. 20. He served in the Army for more than 30 years before his post at the helm of the National Security Council. (Peter Stevenson/The Washington Post)

McMaster’s worldview is in direct conflict with Trump’s on these questions

1) Is Russia an ally or a threat? 

Questions about the first national security adviser Michael Flynn’s conversations with Russian officials ended his tenure within the Trump administration’s first month. By contrast, McMaster says the greatest security threat facing the United States comes from strong states — Russia and China — that are “endeavoring to collapse” the post-World War II economic and security order.

McMaster emphasizes Russian “political subversion, disinformation, and propaganda,” in stark contrast with President Trump’s failure to condemn Russia’s attempt to hack the U.S. election. McMaster says there is no greater military threat than a war among great powers.

2) Should the United States go it alone in world affairs?

Because McMaster sees Russia actively trying to assert dominance, he values U.S. involvement in NATO. He calls it “arrogant and narcissistic” to encourage the United States to disengage from the world’s problems, because that examines global issues only as they relate to the United States, and he criticizes isolationism more generally.

Joint multinational operations are the appropriate response to the “fallacy” that the United States can withdraw from the world and go it alone, McMaster argues. Further, he argues that military power works to keep Americans safe only if well-integrated with “all elements of national and international power,” referring specifically to the safety of alliances.

3) What’s the best way to respond to Islamist terrorism?

McMaster and Trump have very different understandings of the right strategic response to terrorism. Trump has lamented that the United States did not take Iraq’s oil and quipped that terrorists’ family members should be targeted. By contrast, in Iraq, McMaster developed counterinsurgency doctrines in which soldiers worked not just to destroy targets but to protect populations and win local communities’ hearts and minds.

Trump speaks of terrorism and Islam as if they were nearly synonymous. On the record, he has stated that “Islam hates us” and that there is “tremendous hatred” within the religion itself. McMaster discusses Islam in a manner consistent with the tactful U.S. foreign policy formulation that’s been used over the last decade. He refers to militant Islamists with the moniker “salafi jihadists” — referring to the Islamist ideal of restoring a bygone glory. McMaster says such practices have a “perverted” and “irreligious interpretation” of Islam.

For McMaster, the sources of Middle Eastern angst are primarily political. He explains the Afghanistan and Iraq insurgencies through a narrative of grievances exacerbated by “ethnic, tribal, and sectarian polarization.” As a student of the 19th-century German military thinker Carl von Clausewitz, McMaster is wary of promising fast and cheap victories.

4) How should U.S. military leaders relate to civilian leaders?

But McMaster’s beliefs about the job he’s taking on — that of a military adviser to the president — may surprise Trump most. McMaster’s book “Dereliction of Duty” is common reading both in military circles and among scholars of civil-military relations. There he places a great deal of blame for the U.S. failures in Vietnam on the Joint Chiefs of Staff who neglected to check an overconfident president and his cadre of top aides.

In that book, McMaster wrote of a president “[p]rofoundly insecure and distrustful of any but his closest civilian advisers.” When President Lyndon B. Johnson faced a decision in Vietnam, McMaster writes, he did so “without the benefit of effective military advice.” The resulting policies were “based on the pursuit of his own political fortunes and his beloved domestic programs” — and not on a sound national security strategy.

Trump cherishes loyalty, as we saw just this week when he fired a top National Security Council appointee for criticizing him in a private speech. We will see whether McMaster will be able to influence decisions when his positions are so strongly at odds with those of the president and his chief advisers.

Sean P. Braniff is a PhD candidate in political science at the University of Notre Dame.