In August 1965, a resolute President Lyndon Johnson said: “America wins the wars that she undertakes. Make no mistake about it.” But the strategy on which he committed America to its ill-fated intervention in Vietnam that year did not aim at winning, but at not losing. McGeorge Bundy, Johnson’s national security adviser, later admitted as much to a biographer, saying that he had personally approved a strategy that used just enough military pressure to achieve a battlefield stalemate, which “would eventually compel the Vietnamese Communists to compromise their objectives,” forcing them to the negotiating table or to a Korea-style armistice.

Bundy added that his strategy rested, in hindsight, on “little more than an unexamined assumption.” The same might be said of President Trump’s newest policy on Afghanistan. Secretary of State Rex Tillerson said that the strategy, which commits a few thousand more troops, was “intended to put pressure on the Taliban.” The idea, he said, was “to have the Taliban understand, you will not win a battlefield victory — we may not win one, but neither will you — so at some point, we have to come to the negotiating table and find a way to bring this to an end.”

There are two great lessons of Vietnam that the Trump administration might bear in mind before attempting to reprise the stalemate strategy that so conspicuously failed in the earlier conflict.

The first was formulated by a rueful Bundy, many years after the end of the Vietnam War: “We ought not to ever be in a position where we are deciding, or undertaking to decide, or even trying to influence the internal power structure” of another country, he told his biographer, Gordon M. Goldstein. George Kennan, the historian and former diplomat, came to the same conclusion long before Bundy. In the Fulbright hearings on Vietnam in February 1966, he stated, “Our country should not be asked, and should not ask of itself, to shoulder the main burden of determining the political realities in any other country.”