Retired Marine Gen. James Mattis made headlines during the 2003 invasion of Iraq when he fired an officer he felt wasn’t pushing fast enough toward Baghdad, a decision those familiar with the incident say was in character for a commander nicknamed “Mad Dog.”

That the Marines didn’t stop says everything about Mattis, a possible choice of President-elect Donald Trump for defense secretary.

Those who know him say he’d be great for the job as the Pentagon’s top civilian — maybe the one most likely to succeed — but some add a caveat.

“He’s decisive, I’m telling you,” said retired Air Force Brig. Gen. Michael Longoria, who commanded all close-air support teams during the invasion. “The question is, can he make that transition? His combat acumen is off the charts because decisiveness in combat, right or wrong, is 99 percent of the challenge.”

A thoughtful, complicated and occasionally profane man, Mattis was quoted by the San Diego Union-Tribune as saying there are “some (people) in the world that just need to be shot,” and was quoted by an NBC affiliate in California at a 2005 panel discussion saying Afghan men who “slap women around … ain’t got no manhood left anyway. So it’s a hell of a lot of fun to shoot them.”

But Mattis also was known to admonish his Marines to think before they opened fire.

Those who know him say he’s an old-school warrior skeptical of the promise of high-tech weapons and aware of the fog of war — the uncertainty of orchestrating events on a battlefield.

“We always called him the ‘warrior monk’ for his tendency to read through things,” said Gen. Mark Welsh III, a recently retired Air Force chief of staff.

One mentor, retired Marine Lt. Gen. Paul Van Riper, said Mattis knows that war is a “bloody, chaotic, uncertain, dangerous environment. Always has been, always will be.”

He described his friend as a student of U.S. government, a reader of classical and contemporary history — likely to carry a copy of “On War” in his rucksack, the 1832 treatise by Prussian strategist Carl von Clausewitz — and dismissive of comfort.

“He is happier in a tent than in a house, happier with boots on than spit-shined shoes,” said Van Riper, 78, of Williamsburg, Virginia.

Writer Thomas E. Ricks described Mattis in his book “The Generals” as a commander willing to share the privations of his grunts.

“One chilly night in Afghanistan late in 2001, Nathaniel Fick, a young Marine officer, was checking on the sentries in his outposts when, after midnight, he spotted three heads in a fighting hole when there should have been just two,” Ricks wrote.

The third man turned out to be Mattis, “leaning against some sandbags, talking with a sergeant and a lance corporal.” Fick was impressed.

Amid admiration, concern

Now studying national security issues at the Hoover Institution, Mattis retired from the corps three years ago, not the required seven for a Cabinet post, so he would need a waiver from the Senate Armed Services Committee chaired by U.S. Sen. John McCain, R-Arizona.

The rule was designed “to preserve the image if not the reality of civilian control,” observed Adm. Bob Inman, a former National Security Agency director who’s now the Lyndon B. Johnson Centennial Chair in National Policy at the University of Texas at Austin.

Doubters who count themselves as friends and admirers of Mattis say they’re uneasy about him getting a waiver.

“It’s something that I would be concerned about because we believe so much in the military being subservient to civilian leadership,” said Longoria, a Houston native who now lives in Carrolton, Virginia.

Even fans of Mattis like Van Riper have qualms about it. A company commander in Vietnam who later led the Marine Corps Combat Development Command, he said Mattis is the best candidate to head the Defense Department, but added: “I want to qualify that because, philosophically, I think it should be a civilian even if the civilian had less skills. Our tradition has been that our military is led by civilians.”

Another issue in play for Lt. Gen. Guy Swan, a former commander of U.S. Army North, is that Mattis isn’t the only general being considered for an administration job. Trump’s transition team is interviewing a half-dozen of them, according to news reports, including retired Marine Gen. John Kelly to head the Homeland Security Department. The president-elect already has picked retired Army Lt. Gen. Michael Flynn, former head of the Defense Intelligence Agency, to serve as national security adviser.

“I think that Gen. Mattis is a fine leader and has a lot of the strategic and even some of the political skills that are needed for that job, so on the face of it taken as a single issue, I’m reasonably supportive of that,” said Swan, vice president for education for the Association of the U.S. Army. “But the concern that I have, and I’ve heard it expressed by some other officers, is this perception that the Trump team is looking at a number of military officers for key positions in the government.”

Different from Trump

Trump, in an interview this week with the New York Times, expressed no worries over the issue, saying: “I think it’s time, maybe, it’s time for a general.”

Describing Mattis as a “strong, highly dignified man,” he also said they disagreed over the waterboarding of prisoners.

“I said, what do you think of waterboarding? He said — I was surprised — he said, ‘I’ve never found it to be useful.’ He said, ‘I’ve always found, give me a pack of cigarettes and a couple of beers and I do better with that than I do with torture.’ And I was very impressed by that answer. I was surprised, because he’s known as being like the toughest guy,” Trump said.

A moment later, Trump added, “I thought he would say — you know he’s known as Mad Dog Mattis, right? Mad Dog for a reason. I thought he’d say, ‘It’s phenomenal, don’t lose it.’”

As defense secretary, Mattis would work with the president, secretary of state and national security adviser. He would deal with the civilian service secretaries, Joint Chiefs of Staff and the heads of unified combat commands.

Inman — who himself was nominated by President Bill Clinton to be defense secretary but withdrew from consideration in January 1994 — said Mattis’ biggest challenge might be dealing with former peers who now would be his subordinates.

“The real issue for a secretary of defense,” Inman added, “is the relationship with the president.”

That’s an unknown. If Trump and Mattis both are prone to make controversial, off-color comments, their lives and habits in some ways couldn’t be more different.

Trump took multiple draft deferments during the Vietnam War. Mattis enlisted in the Marines in 1969. Trump is nominally an author but his books are written with the help of others, and he has said he didn’t have the time to get through others’ books in their entirety.

Mattis and retired Army Gen. David Petraeus oversaw the publication of FM 3-24, the Army-Marine Counterinsurgency Manual, a blueprint for pacifying Iraq and Afghanistan. Goodreads.com said Mattis listed 69 books on his professional reading list, running from “The Arab Mind” to “Afghan Guerrilla Warfare: In the Words of Mujahideen Fighters.”

Trump told a debate audience in New Hampshire early this year that he would restore waterboarding. He didn’t back off that position this week, telling the Times, “If it’s so important to the American people, I would go for it,” but suggested Mattis had given him something to think about.

Retired Air Force Gen. Eugene Habiger of a San Antonio, a former head of the U.S. Strategic Command, predicted that Mattis would not need to countermand potentially illegal orders by Trump.

“Our republic is too strong and we have too many safeguards,” he said. “I’m not concerned about a rogue president.”

Swan, 62, of Arlington, Virginia, said Mattis would help soothe those who fear Trump as commander-in-chief, calling him “a straight shooter with very strong values about democracy, about the role of the armed forces in a democracy.”

Van Riper, in turn, said Mattis’s character is the ultimate safeguard.

“He would always do what’s right,” he said. “He would honor the Constitution. He understood his oath to the Constitution at the start.”

sigc@express-news.net