Sen. John Warner's Foxhole Doctrine: Democrat or Republican, we're all fellow soldiers.

John Warner, the former senator, Navy secretary and World War II and Korean War veteran who died last month at 94, will be honored Wednesday with a funeral at National Cathedral. We knew him as an enthusiastic adviser to With Honor Action, a cross-partisan organization working to reduce polarization and dysfunction in Congress by advancing principled veteran leadership.

In Warner’s final months, we shared a series of life history interviews with him, during which he illuminated the principle that guided him over his decades of public service. He called it the “Foxhole Doctrine,” and believed it was the key to our future.

He first learned the doctrine from his father, John Warner II, a doctor who treated soldiers on the front lines of the bloody battlefields of World War I.

“He taught me the military principles,” Sen. Warner recalled. “Duty, honor, country. That’s the code which you have got to live up to. You’ve got to establish a trusting relationship with your fellow soldiers.”

Causes larger than any one person

Warner’s father explained to him that when you are in a foxhole fighting for your country, you look after each other. You fight for a common cause larger than any one individual, transcending any differences you have in background or belief. That lesson constitutes the heart of the Foxhole Doctrine.

At age 17, Warner wanted to join in the action himself, as a Marine in World War II. His father resisted. “He had seen too many Marines destroyed in World War I. It haunted him.” Warner persisted and finally received his father's permission to enlist in the Navy. Years later, after his father had passed away, Warner signed up for the Marine Corps and served in the Korean War.

“The loss of your pals is what you carry back with you,” he said. “It’s hard to be in a tent when the tent used to have five guys in it.”

Warner spent most of his life in the arena of national public service, including three decades as Virginia’s Republican senator and chairman of the Senate Armed Services Committee. The Foxhole Doctrine guided him in Congress just as it did in uniform. “It carried over from the military,” he said. “So many of us had been in World War II. We had the doctrine that we had to get things done together.”

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He noted often that while veterans once represented 70% of Congress, they now compose less than 20%.

Warner put aside party lines at many high-pressure moments. These decisions included opposing the Supreme Court nomination of Robert Bork, voting to acquit President Bill Clinton on one of two articles of impeachment, critiquing the execution of the Iraq War and in 2014 endorsing his onetime rival, Democrat Mark Warner, for his old Senate seat. Two years later, the Republican endorsed Hillary Clinton for president.

“I didn’t get anything done by pulling out my sword and cutting everybody in my pathway,” he told us. “Bipartisanship is something we can and must strive for. It’s what is best for the country.”

Fewer veterans and more dysfunction

One of Warner’s strongest relationships was with his Democratic counterpart on the Armed Services Committee, Sen. Sam Nunn of Georgia: “We always tried to paddle with the same strokes, as you do in canoeing.” Some of his colleagues threatened to remove him from leadership if he kept working so closely with Nunn.

“I had only the best interest of the country in mind,” he recalled, “and so long as I knew Sam did too, we would keep paddling forward in that direction together. We paddled together against many storms from his party and from mine and we both paid a price for it.” In 1996, Warner overcame a formidable insurgent primary campaign.

Over the course of his career, the percentage of veterans in Congress declined while polarization and dysfunction rose. Though Congress has always been one of America’s most visible foxholes, the Jan. 6 insurrection made the metaphor too palpable.

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In our final interview, Sen. Warner looked to the future and considered how to rebuild. He saw his life as a link in a chain of public service, taking particular pride in the For Country Caucus, a group of two dozen veterans in Congress that With Honor Action supports. Its Democratic and Republican members pledge to work together and serve with integrity, civility and courage.

“I see a direct correlation between what the World War II class achieved and what some of today’s veterans are trying to achieve,” Sen. Warner said. “Members of the other party are not our enemies. They are our fellow soldiers.”

Rye Barcott (@ryebarcott) is co-founder and CEO of With Honor Action, and the author of "It Happened on the Way to War." Matthew Wigler (@mattwigler) is a With Honor fellow and teaches politics at Eton College in the United Kingdom.

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This article originally appeared on USA TODAY: Country over party in war and politics: John Warner's Foxhole Doctrine