© Army Sgt. Amber I. Smith/DOD/ALAMY

In late November 2016, I was enjoying Thanksgiving break in my hometown on the Columbia River in Washington state when I received an unexpected call from Vice President-elect Mike Pence. Would I meet with President-elect Donald Trump to discuss the job of secretary of defense?
I had taken no part in the election campaign and had never met or spoken to Mr. Trump, so to say that I was surprised is an understatement. Further, I knew that, absent a congressional waiver, federal law prohibited a former military officer from serving as secretary of defense within seven years of departing military service. Given that no wavier had been authorized since Gen. George Marshall was made secretary in 1950, and I’d been out for only 3½ years, I doubted I was a viable candidate. Nonetheless, I felt I should go to Bedminster, N.J., for the interview.
I had time on the cross-country flight to ponder how to encapsulate my view of America’s role in the world. On my flight out of Denver, the flight attendant’s standard safety briefing caught my attention: If cabin pressure is lost, masks will fall…Put your own mask on first, then help others around you. In that moment, those familiar words seemed like a metaphor: To preserve our leadership role, we needed to get our own country’s act together first, especially if we were to help others.
The next day, I was driven to the Trump National Golf Club and, entering a side door, waited about 20 minutes before I was ushered into a modest conference room. I was introduced to the president-elect, the vice president-elect, the incoming White House chief of staff and a handful of others. We talked about the state of our military, where our views aligned and where they differed. Mr. Trump led the wide-ranging, 40-minute discussion, and the tone was amiable.
Afterward, the president-elect escorted me out to the front steps of the colonnaded clubhouse, where the press was gathered. I assumed that I would be on my way back to Stanford University’s Hoover Institution, where I’d spent the past few years doing research. I figured that my strong support of NATO and my dismissal of the use of torture on prisoners would have the president-elect looking for another candidate.
Standing beside him on the steps as photographers snapped away, I was surprised for the second time that week when he characterized me to the reporters as "the real deal." Days later, I was formally nominated.
During the interview, Mr. Trump had asked me if I could do the job. I said I could. I’d never aspired to be secretary of defense and took the opportunity to suggest several other candidates I thought highly capable. Still, having been raised by the Greatest Generation, by two parents who had served in World War II, and subsequently shaped by more than four decades in the Marine Corps, I considered government service to be both honor and duty. When the president asks you to do something, you don’t play Hamlet on the wall, wringing your hands. To quote a great American company’s slogan, you "just do it." So long as you are prepared, you say yes.
When it comes to the defense of our experiment in democracy and our way of life, ideology should have nothing to do with it. Whether asked to serve by a Democratic or a Republican, you serve. "Politics ends at the water’s edge": That ethos has shaped and defined me, and I wasn’t going to betray it, no matter how much I was enjoying my life west of the Rockies and spending time with a family I had neglected during my 40-plus years in the Marines.
When I said I could do the job, I meant I felt prepared. I knew the job intimately. In the late 1990s, I had served as the executive secretary to two secretaries of defense, William Perry and William Cohen. In close quarters, I had gained a personal grasp of the immensity and gravity of a "secdef’s" responsibilities. The job is tough: Our first secretary of defense, James Forrestal, committed suicide, and few have emerged from the job unscathed, either legally or politically.
We were at war, amid the longest continuous stretch of armed conflict in our nation’s history. I’d signed enough letters to next of kin about the death of a loved one to understand the consequences of leading a department on a war footing when the rest of the country was not. The Department of Defense’s millions of devoted troops and civilians spread around the world carried out their mission with a budget larger than the GDPs of all but two dozen countries.
On a personal level, I had no great desire to return to Washington, D.C. I drew no energy from the turmoil and politics that animate our capital. Yet I didn’t feel overwhelmed by the job’s immensities. I also felt confident that I could gain bipartisan support for the Department of Defense despite the political fratricide practiced in Washington.
My career in the Marines brought me to that moment and prepared me to say yes to a job of that magnitude. The Marines teach you, above all, how to adapt, improvise and overcome. But they expect you to have done your homework, to have mastered your profession. Amateur performance is anathema.
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The Marines are bluntly critical of falling short, satisfied only with 100% effort and commitment. Yet over the course of my career, every time I made a mistake—and I made many—the Marines promoted me. They recognized that these mistakes were part of my tuition and a necessary bridge to learning how to do things right. Year in and year out, the Marines had trained me in skills they knew I needed, while educating me to deal with the unexpected.
Beneath its Prussian exterior of short haircuts, crisp uniforms and exacting standards, the Corps nurtured some of the strangest mavericks and most original thinkers I encountered in my journey through multiple commands and dozens of countries. The Marines’ military excellence does not suffocate intellectual freedom or substitute regimented dogma for imaginative solutions. They know their doctrine, often derived from lessons learned in combat and written in blood, but refuse to let that turn into dogma.
Woe to the unimaginative one who, in after-action reviews, takes refuge in doctrine. The critiques in the field, in the classroom or at happy hour are blunt for good reasons. Personal sensitivities are irrelevant. No effort is made to ease you through your midlife crisis when peers, seniors or subordinates offer more cunning or historically proven options, even when out of step with doctrine.
In any organization, it’s all about selecting the right team. The two qualities I was taught to value most were initiative and aggressiveness. Institutions get the behaviors they reward.
During my monthlong preparation for my Senate confirmation hearings, I read many excellent intelligence briefings. I was struck by the degree to which our competitive military edge was eroding, including our technological advantage. We would have to focus on regaining the edge.
I had been fighting terrorism in the Middle East during my last decade of military service. During that time, and in the three years since I had left active duty, haphazard funding had significantly worsened the situation, doing more damage to our current and future military readiness than any enemy in the field.
I could see that the background drummed into me as a Marine would need to be adapted to fit my role as a civilian secretary. It now became even clearer to me why the Marines assign an expanded reading list to everyone promoted to a new rank: That reading gives historical depth that lights the path ahead. Books like the "Personal Memoirs of Ulysses S. Grant," "Sherman" by B.H. Liddell Hart and Field Marshal William Slim’s "Defeat Into Victory" illustrated that we could always develop options no matter how worrisome the situation. Slowly but surely, we learned there was nothing new under the sun: Properly informed, we weren’t victims—we could always create options.
Fate, Providence or the chance assignments of a military career had me as ready as I could be when tapped on the shoulder. Without arrogance or ignorance, I could answer yes when asked to serve one more time.
When I served as Supreme Allied Commander Transformation, a new post created in 2002 to help streamline and reform NATO’s command structure, I served with a brilliant admiral from a European nation. He looked and acted every inch the forceful leader. Too forceful: He yelled, dressing officers down in front of others, and publicly mocked reports that he considered shallow instead of clarifying what he wanted. He was harsh and inconsiderate, and his subordinates were fearful.
I called in the admiral and carefully explained why I disapproved of his leadership. "Your staff resents you," I said. "You’re disappointed in their input. OK. But your criticism makes that input worse, not better. You’re going the wrong way. You cannot allow your passion for excellence to destroy your compassion for them as human beings." This was a point I had always driven home to my subordinates.
"Change your leadership style," I continued. "Coach and encourage; don’t berate, least of all in public."
But he soon reverted to demeaning his subordinates. I shouldn’t have been surprised. When for decades you have been rewarded and promoted, it’s difficult to break the habits you’ve acquired, regardless of how they may have worked in another setting. Finally, I told him to go home.
An oft-spoken admonition in the Marines is this: When you’re going to a gunfight, bring all your friends with guns. Having fought many times in coalitions, I believe that we need every ally we can bring to the fight. From imaginative military solutions to their country’s vote in the U.N., the more allies the better. I have never been on a crowded battlefield, and there is always room for those who want to be there alongside us.
A wise leader must deal with reality and state what he intends, and what level of commitment he is willing to invest in achieving that end. He then has to trust that his subordinates know how to carry that out. Wise leadership requires collaboration; otherwise, it will lead to failure.
Nations with allies thrive, and those without them wither. Alone, America cannot protect our people and our economy. At this time, we can see storm clouds gathering. A polemicist’s role is not sufficient for a leader. A leader must display strategic acumen that incorporates respect for those nations that have stood with us when trouble loomed. Returning to a strategic stance that includes the interests of as many nations as we can make common cause with, we can better deal with this imperfect world we occupy together. Absent this, we will occupy an increasingly lonely position, one that puts us at increasing risk in the world.
It never dawned on me that I would serve again in a government post after retiring from active duty. But the phone call came, and on a Saturday morning in late 2017, I walked into the secretary of defense’s office, which I had first entered as a colonel on staff 20 years earlier. Using every skill I had learned during my decades as a Marine, I did as well as I could for as long as I could. When my concrete solutions and strategic advice, especially keeping faith with our allies, no longer resonated, it was time to resign, despite the limitless joy I felt serving alongside our troops in defense of our Constitution.
Unlike in the past, where we were unified and drew in allies, currently our own commons seems to be breaking apart. What concerns me most as a military man is not our external adversaries; it is our internal divisiveness. We are dividing into hostile tribes cheering against each other, fueled by emotion and a mutual disdain that jeopardizes our future, instead of rediscovering our common ground and finding solutions.
All Americans need to recognize that our democracy is an experiment—and one that can be reversed. We all know that we’re better than our current politics. Tribalism must not be allowed to destroy our experiment.
Toward the end of the Marjah, Afghanistan, battle in 2010, I encountered a Marine and a Navy corpsman, both sopping wet, having just cooled off by relaxing in the adjacent irrigation ditch. I gave them my usual: "How’s it going, young men?"
"Living the dream, sir!" the Marine shouted. "No Maserati, no problem," the sailor added with a smile.
Their nonchalance and good cheer, even as they lived one day at a time under austere conditions, reminded me how unimportant are many of the things back home that can divide us if we let them.
On each of our coins is inscribed America’s de facto motto, "E Pluribus Unum"—from many, one. For our experiment in democracy to survive, we must live that motto.
—Gen. Mattis served as secretary of defense during the Trump administration and served in the U.S. Marine Corps for more than four decades. This essay is adapted from his forthcoming book "Call Sign Chaos: Learning to Lead," co-authored with Bing West, which will be published Sept. 3 by Random House.
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