President Donald Trump with Army Lt. Gen. H.R. McMaster at Trump's Mar-a-Lago estate. AP US President Donald Trump's new national security adviser, Lt. Gen H. R. McMaster, has a reputation as a "warrior-scholar" and positions that make him appear an almost complete reversal from Michael Flynn.

Throughout his career, McMaster has established himself as a hawk against Russia's leveraging of geopolitical power to further its influence and a defender of the integrity of Muslim civilians caught up in the US's Middle Eastern campaign.

As the director of the Army Capabilities Integration Center, McMaster worked on envisioning the Army's structure in 2025 and beyond, which means countering the growing, multifaceted threat from Russia.

In a 2016 speech to the Virginia Military Institute, McMaster stressed the need for the US to have "strategic vision" in its fight against "hostile revisionist powers" — such as Russia, China, North Korea, and Iran — that "annex territory, intimidate our allies, develop nuclear weapons, and use proxies under the cover of modernized conventional militaries."

McMaster's speech framed the issue around geopolitics instead of military strategy or deployments.

"Geopolitics have returned as US rivals from Europe to the greater Middle East to East Asia attempt to collapse the post-WWII economic and security order," McMaster said.

In McMaster's view, the US needs to establish what a "win" means when it comes to threats, including nonmilitary sources of leverage.

"Establishing an objective other than winning is not only counterproductive but also irresponsible and wasteful. Under some circumstances, an objective other than winning is unethical," McMaster said at the VMI, evoking his past criticisms of the Iraq and Vietnam wars.

A statue of Saddam Hussein falling in central Baghdad in 2003. REUTERS/Goran Tomasevic

In 1997, McMaster published "Dereliction of Duty" on the strategic failures of the Vietnam War; the book was part of his Ph.D. thesis at the University of North Carolina at Chapel Hill. Rep. Adam Schiff, a Democrat from California, said in a tweet that McMaster "wrote the book on importance of standing up" to the president.

McMaster doesn't fall in line with the hardline view of Muslims held by Flynn and White House chief strategist Steve Bannon that led Trump to issue an executive order banning immigration and travel from seven majority-Muslim nations.

In an interview with NPR, Schiff said McMaster once began "dressing down" a subordinate who suggested that the Afghan military officials the US was working with had an "innate tendency" toward corruption.

At the 2016 VMI speech, McMaster blamed groups like ISIS for "cynically use a perverted version of religion," to push their hardline beliefs.

A gathering in the Oval Office during a telephone call between Trump and Russian President Vladimir Putin. Pete Marovich/Pool via CNP/MediaPunch/IPX

This contrasts sharply with Flynn, who once tweeted that "Fear of Muslims is RATIONAL" and included a link to a YouTube video that claims the religion of Islam wants "80% of people enslaved or exterminated."

Ultimately, it was Flynn's relationship with Russia that brought about his resignation, as he was accused of misleading Vice President Mike Pence about a call with the Russian ambassador to the US in which Flynn had discussed easing of Obama-era sanctions against Moscow.

On the National Security Council, McMaster will have to contend with Bannon and senior adviser Stephen Miller, authors of Trump's immigration ban.