Sen. John McCain (R-Ariz.) speaks during a Senate Foreign Relations Committee hearing in 2013. (Susan Walsh/AP)

It didn’t matter how many stars were on their epaulets. It didn’t matter what heroic acts they had performed on the battlefield. 

When Sen. John McCain was questioning the nation’s generals and admirals on Capitol Hill, the gloves came off. 

“So, basically, general, what you’re telling us is that everything is fine as we see hundreds and thousands of refugees leave and flood Europe, as we see, now, 250,000 Syrians slaughtered?” McCain asked the top U.S. general in charge of the Middle East in 2015.

“Of course, then, the question springs to mind: What else didn’t you investigate? If we didn’t investigate a gross and egregious violation such as that,” he said during the fallout to the Abu Ghraib prisoner abuse scandal in Iraq in 2004.

“Gentlemen, the credibility gap between you and Congress is as wide as the Grand Canyon.” That was in the 1990s, regarding the presence of U.S. troops in Bosnia.

Such questions and comments were typical of the Arizona Republican’s approach in the Senate, where he served as a member of the Armed Services Committee for more than three decades and since 2015 as chairman of the powerful committee overseeing the military.

The top military brass and civilian leaders at the Pentagon knew that McCain, who died Saturday at the age of 81, would be tough when they came to the chamber to testify. He often narrowed his eyes as they dissembled under his questioning.

McCain’s political career earned him a reputation as a hawkish advocate of military intervention and an impassioned supporter of the American armed services. Even so, the retired Navy captain and pilot hardly ever gave the Pentagon leadership a pass. 

Retired Adm. Mike Mullen, former chairman of the Joint Chiefs of Staff, recalled McCain in a statement as “resolute in his beliefs, even pugnacious,” and praised him as a lion who was never too busy to consider the views of others and who “in the heat of fierce political debate never lost sight of what was the most important: our American experiment.”

The son and grandson of Navy admirals, and a prisoner of war for 5½ years in Vietnam, McCain earned the credibility to force even the most decorated American officials to explain themselves and their decisions to the public in front of the Senate. McCain took his oversight duties seriously and regularly tested his die-hard views against theirs in public exchanges, often prying loose uncomfortable truths the military would rather have kept under wraps. 

While some of his fellow lawmakers could be deferential to the Pentagon brass, McCain believed that military leaders had an even greater responsibility to explain themselves, because they were putting American lives at risk and representing the nation’s values overseas. While serving in Vietnam, McCain had become acutely aware of the military’s tendency to put a positive spin on uncomfortable truths when watching the press briefings that became known as the “Five O’Clock Follies.”

“McCain just thought the stakes are so big,” said his former foreign policy adviser, Richard Fontaine. “Too much deference is not a good practice.”

The senator had no problem crusading against miliary leaders for one reason or another, and even those he clashed with most sharply expressed respect for his intentions. Retired Gen. Martin Dempsey, the former chairman of the Joint Chiefs of Staff whom McCain once derided as the “most disappointing chairman he had ever seen,” praised McCain as a leader. 

“Senator McCain was particularly passionate about America’s roles and responsibilities in the world,” he wrote. “An astute student of history, he knew that ‘domestic policy can only defeat us; foreign policy can kill us’ (JFK). American foreign policy has lost its greatest champion.”

Retired Gen. Michael Hayden, the former director of the CIA whom McCain accused in his recent book of misleading the White House and Congress about the effectiveness of the agency’s “enhanced interrogation techniques,” called the senator a hero.

“While I was at CIA, Senator JOHN McCain ripped me a new one on several occasions,” Hayden said in a tweet Sunday. “But not once did he think I shouldn’t have a security clearance. Go figure. RIP, American hero.”

McCain’s combative approach was infectious for some. Sen. Lindsey O. Graham (R-S.C.), his chief acolyte, in recent years has become known on the Armed Services Committee for his unforgiving interrogations of Pentagon leaders, often with yes-or-no questions.

McCain could be brutal and crushing when top officers made mistakes but also stood by those he respected despite personal and sometimes high-profile public failings. He was effusive in his praise for the generals he liked, those who shared his view of American power and how it should be wielded.

He called Gen. David Petraeus “one of the great military leaders in American history,” and continued to praise him even after the retired Army general resigned from the CIA directorship over the improper handling of classified information during an extramarital affair.

“I think people make mistakes in life and you move on,” McCain said as he advocated for President Trump to choose Petraeus as secretary of state.

In an interview with ABC News this weekend, Petraeus said that “no one had the backs” of American service members more than McCain and that “no one did more to assure that they had what was needed to prevail on the battlefield.” 

McCain, a two-time presidential candidate, traveled abroad to meet aspiring democratic leaders in foreign states and American troops in combat zones, part of a commitment to developing his own opinions about what the nation should or should not be doing overseas. He often requested to meet troops lower down in the chain of command and stationed outside capitals as he sought to test the veracity of what top generals were telling him.

McCain took a Manichaean view of foreign affairs, looking to put American military might behind those professing the advancement of democratic values and against those violating those ideals. He believed in human rights and international compacts such as the Geneva Conventions and cared whether the military was upholding them.

Beginning and after the torture scandals during the George W. Bush years, McCain led an effort against the Pentagon and many Republican colleagues to end torture and push through higher standards for interrogation.

“They are threatening to weaken the Geneva Conventions,” McCain said in 2006, according to Fontaine. “I can’t let them do that. I’ll fight them to the end — even if it costs me everything.”

McCain ultimately prevailed.

The senator looked inward as well as outward, mastering the details of the American military bureaucracy and acquisition system and throwing his weight behind measures that changed the face of the armed services. It was the kind of in-the-trenches legislative work, combating acquisition waste and reorganizing military retirement benefits, that would cause other legislators’ eyes to glaze over.

He railed against defense acquisition gone awry, whether it was the Navy’s littoral combat ship or the joint-service F-35 fighter jet. Seizing upon the much-criticized F-22 Raptor, McCain once said the military’s “168 F-22s, costing over $200 million each, may very well become the most expensive corroding hangar queens in the history of modern military aviation.”

Lately, he had crusaded to fix what he called a readiness crisis in the American military, with aging equipment, inconsistent funding and a force exhausted from 17 years of regular deployments. Lawmakers named this year’s defense policy bill after McCain. The $716 billion bill sought to address those issues with raises, equipment renewals and better funding for personnel and maintenance.

Earlier this month, in an appearance at New York’s Fort Drum, Trump signed the legislation, formally named the John S. McCain National Defense Authorization Act for Fiscal Year 2019. The president made no public mention of McCain.