With a new administration and president so unlike anything we have seen before, it may seem fruitless to try to draw any instruction from the past. But there’s one lesson, almost half a century old, that raises what may well be the most fundamental question about the Trump presidency—a question that could well be literally a matter of life and death.

In early 1968, the Vietnam War had become a quagmire. More than 500,000 Americans were in combat there; 500 were dying every week. Dissent was spreading not only on college campuses, but also within the Democratic Party. A peace candidate, Minnesota Senator Eugene McCarthy, was mounting a primary challenge to President Lyndon Johnson.

When Johnson realized that Defense Secretary Robert McNamara was increasingly plagued by doubt, he replaced him with Clark Clifford, the consummate Washington lawyer-lobbyist, who had been a key counselor in Democratic Party affairs for 20 years, as well as a highly paid lawyer with blue-chip corporate clients. After the 1960 election, President Kennedy said of Clifford’s assistance, “All he asked in return was that we advertise his law firm on the backs of one-dollar bills.”

Clifford had been one of Johnson’s more hawkish confidants as the war escalated, but within days of his nomination, the Tet Offensive—a series of  attacks by North Vietnamese and Viet Cong forces across South Vietnam—had shaken U.S. confidence that there was a light at the end of the tunnel. When the Pentagon asked for an increase of 206,000 troops, Johnson asked Clifford to chair a task force to probe exactly where and how the troops would be deployed. The result was a revelation.

“I know for three full days I spent down in the tank with the Joint Chiefs of Staff, where you sit with all of the communications devices that go all over the world,” Clifford recalled years later in a PBS television interview. “We had long talks. How long would it take? They didn’t know. How many more troops would it take? They didn’t know. Would 206,000 answer the demand? They didn’t know. Might there be more? Yes, there might be more. So, when it was all over, I said, ‘What is the plan to win the war in Vietnam?’ Well, the only plan is that ultimately the attrition will wear down the North Vietnamese and they will have had enough. Is there any indication that we’ve reached that point? No, there isn’t. ...