Hagel and McCain were two of several combat veterans on stage during Tuesday’s Senate Foreign Relations Committee hearing about whether to authorize military strikes on Syria in retaliation for its chemical weapons use. And where politics meets global security, combat experience quickly became a qualifying credit several times during the debate.

It showed after Sen. Rand Paul, R-Ky., had his spotlight moment to lecture Secretary of State John Kerry about the war powers given to the Congress by the constitution, and his limited view of the executive branch. Kerry waited patiently, and then the baritone former senator and anti-war protestor gave an erupting rebuttal, making his case for military strikes into the heart of the Syrian war. Pointing to himself, Hagel, McCain and Joint Chiefs Chairman Gen. Martin Dempsey, who fought in Iraq, Kerry said, “There's not one of us that doesn't understand what going to war means.”

No one ever wants to go to war, Kerry said, in trying to argue that the Obama administration wants Congress’s support only for a limited strike inside Syria, with no ground troops, specifically targeting chemical weapons capabilities.

McCain and Hagel often are lumped together as Vietnam combat veterans, as Kerry did. But they have two strikingly different views of when the use of force is warranted that reflect their experiences of that war. One difference is obvious: McCain spent six years as a prisoner of war in the Hanoi Hilton prison and knows the suffering of war in his way. Hagel spent two years as soldier seeing his share of combat while walking point with his brother Tom. But another distinction has greater relevance today: McCain was a Navy combat pilot. Hagel was an infantryman, who saw close hand the effects of aerial bombing and the rest of warfare.

Neither man is a dove. Hagel staunchly backs a strike against Syria most of America opposes. But Hagel has written about his personal Vietnam battlefield declaration to never permit warfare again, if ever he were in power to prevent it. McCain, on the other hand, has never been accused of being a peacenik. For two years, he has clamored for American military intervention in Syria. Not a ground invasion, clearly, but some combination of airborne strikes and other forceful ways to get the U.S. military involved.

Here is McCain’s view of the Vietnam War. In 1973, he wrote: “The date was Oct. 26, 1967. I was on my 23rd mission, flying right over the heart of Hanoi in a dive at about 4,500 feet, when a Russian missile the size of a telephone pole came up -- the sky was full of them -- and blew the right wing off my Skyhawk dive bomber. It went into an inverted, almost straight-down spin.”

McCain wrote of hating the guards who tortured him and held him in solitary for two years. He directs his hate at the Vietnamese leaders. Hagel, on the other hand, turns towards U.S. leaders.

Hagel, in his 2008 book, America: Our Next Chapter, after surviving his wounds while in Vietnam wrote: “I remember a strong resolve coming over me, as our chopper climbed over the glistening green canopy of the jungle and I watched the steam rise above it in the morning light. I made myself a promise that if I ever got out of that place and was ever in a position to do something about war -- so horrible, so filled with suffering -- I would do whatever I could to stop it. I have never forgotten that promise.”

It’s a promise Hagel repeats to this day. He called himself changed forever, from being “a foot soldier in an ill-conceived, poorly prosecuted, and unsuccessful war.”

“It is the responsibility of every elected official, especially those who have seen combat, to assure that any policy that sends men and women into war is worthy of the sacrifices that we ask of them and their families,” he wrote. It's a mantra he's repeated several times since taking office in February.

In questioning the automatic flag-waving of Americans for the troops, Hagel wrote, “I wonder how many of us here at home actually picture the grunt in the mud and grime with the cold stench of death hanging over him…”

Get the picture? One man prosecuted military strikes from above. The other smelled their effects on the ground.

“Obviously the perspective from 30,000 feet is entirely differently from that on the ground,” said former Sen. Chuck Robb, D-Va. Robb served in Vietnam also, before the Senate, and knew McCain’s father before he knew the senator. Though a distant memory now, Robb described the feeling of walking among dead Americans and their enemies, searching dead North Vietnamese Army soldiers’ bodies for weapons or intelligence only to find their family pictures. Robb was careful to say he would not wade into the Syria debate and was reluctant to speak on the record. But ultimately, he insisted that years of being a policymaker have as much weight on both McCain and Hagel as their combat years.

“Once you’ve been on the policy side, you tend to develop a broader understanding and complete picture of what they’re trying to conduct at any given time,” he said.

McCain, back in ’73, wrote what he’d like to be later in life. “If I have to leave the Navy, I hope to serve the government in some capacity, preferably in Foreign Service for the State Department.”

Just like Kerry.