A "heated exchange." That was how news accounts described a Labor Day weekend conference call dust-up between Secretary of State John Kerry and Minnesota's new member of Congress from the Eighth District, DFLer Rick Nolan.

The topic of the call was Syria. But the flare-up involved Vietnam.

Last week, the Kerry-Nolan rift appeared to be healing. Nolan publicly praised President Obama's willingness to seek congressional approval for military action and to delay a vote while diplomatic efforts press Syria to turn over its poison-gas weapons to international authorities.

But the reportedly intemperate words the congressman and the cabinet secretary exchanged underscored for me something I've long feared about my big baby-boom generation: We'll never get over Vietnam.

For we who came to adulthood while that bloody American misadventure played out between 1963 and 1975, the word still stirs a bitter stew of emotions. It's the biggest U.S. policy mistake of our lifetimes — bigger in U.S. death toll and national psychic damage than latter-day ill-advised wars in Iraq and Afghanistan.

It's the unavoidable prism through which Kerry, Nolan and a lot of the rest of us boomers view U.S. foreign policy in general and today's Syrian dilemma in particular. The fact that Kerry and Nolan were coming down on opposite sides of the Syria question two weeks ago only illustrates what was always true about Vietnam: How one sees it depends on where one stands.

Associated Press, Star Tribune
U.S. Secretary of State John Kerry

Kerry and Nolan once stood side by side. They were antiwar allies — not friends, Nolan said, but acquaintances in the early 1970s as each worked to end a war he detested.

In 1969, Kerry came home from Vietnam with a Bronze Star, a Silver Star, three Purple Hearts and a burning desire to extricate Americans from what he argued was Vietnam's civil war. He became a leader of Vietnam Veterans Against the War and was the first Vietnam veteran to testify before Congress in opposition to U.S. policy.

That same year, social-studies teacher Nolan began a two-term stint in the Minnesota House. While in office, he did not hesitate to participate in antiwar protests, despite the political risk that posed in a district that included the Minnesota National Guard's Camp Ripley.

Kerry and Nolan both ran unsuccessfully for Congress in 1972 on an antiwar platform. Both eventually arrived in Washington — Nolan in 1974, Kerry 10 years later. After a circuitous path, the Vietnam-era allies are together again.

Together in disagreement, that is. Kerry was on the phone with members of Congress to sell the idea that the United States should militarily punish the regime of Syrian President Bashar Assad for killing some 1,400 Syrian civilians with sarin gas.

Nolan was having none of it — or so the tattlers related after the members-only conversation ended — and he angered Kerry by arguing that anyone who knew the lessons of Vietnam ought to know better.

What lessons? I asked Nolan last week. His responded as if he'd been rehearsing his answer for 40 years:

"You need to consider all your options, not just the military option. Recognize the speed by which low-level conflicts can escalate. Also, know that unexpected events can pull these things off course. Launch an attack, you're determined that there will not be boots on the ground — in Vietnam, we said we'd just send advisers — then unexpected events occur. The very same people then say, 'I said that under different circumstances. Now we need to go all in.'

"We've got to recognize the limits of power. The president himself has said we are not the policeman of the world. There are some problems for which there are not immediate solutions. … Vietnam teaches that you have to have meaningful support from the international community, particularly when you are trying to enforce international norms. That's when unilateral military actions are not the tactic to use."

I doubt that Nolan gave that lecture to the secretary of state. But the way he stressed one line has me betting that he hurled it at Kerry: "We're witnessing a case of collective amnesia about the lessons of Vietnam."

Tell someone who earned three Purple Hearts in a war that he's forgotten it, and you're bound to get a rise.

Nolan said he's been surprised by Kerry's eagerness to unleash U.S. military might in Syria. But, he added, he also was surprised 11 years ago, when then-U.S. Sen. Kerry voted to approve military action in Iraq. Kerry had then been in the Senate for 18 years and was gearing up for a presidential bid. In a foreign-policy sense, he had moved to a different place.

By comparison, Nolan left Congress in 1980 and returned this year. The lessons he took from Vietnam weren't mitigated by three intervening decades of Washington policy debates and war machine lobbying. Instead, he said, those lessons were reinforced by a business career that included several years living in the Middle East, where he found that things are seldom as they first appear to American eyes.

Arriving back in Washington with the freedom and self-assurance that goes with being 69 years old, Nolan has no compunction about challenging an old ally if he thinks old mistakes are about to be repeated.

"I've been around to help end several wars now, most of which were mistakes," he said. "I'll do everything I can to stop another one before it happens." He's back on the peace train.

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Lori Sturdevant is a Star Tribune editorial writer and columnist. She is at lsturdevant@startribune.com.