It’s no wonder — as we near the mark of three years since America surrendered Afghanistan to the Taliban — that President Biden neglected to mention in his valediction at Chicago his top foreign policy fiasco. Chalk it up to the fact that, despite Mr. Biden’s promise upon retreating from Kabul that Afghanistan would “never be used again to launch an attack on our homeland,” the threat is again, as it was before September 11, waxing.

That, at least, is the appraisal of, among others, the sages at the nonpartisan United States Institute of Peace, which recently warned that “terrorist threats to US interests” from both Afghanistan and its neighbor Pakistan “are steadily rising.” Even worse, the institute cautions, the chaos in Afghanistan “presents growing opportunities for terrorist groups compared to the period before the U.S. withdrawal,” courtesy of Mr. Biden.

This is because America took its eye off the ball in Afghanistan after Mr. Biden’s botched withdrawal, which saw American forces leave to the enemy billions of dollars’ worth of matériel — and abandon our Afghan allies to the tender mercies of the Taliban. It was a stain on America’s national honor on a par with the pell-mell retreat from Saigon in 1975, when freedom-loving South Vietnamese scrambled to escape the Communists who had encircled the city.

Mr. Biden was old enough in 2021 to know better — even if his naïveté in 1975 hardly excused his callousness toward the plight of the Free Vietnamese. The 32-year-old freshman senator was summoned then for a briefing at the White House on Vietnam. Mr. Biden startled his colleagues with a “didactic performance” insisting that the situation was “hopeless” and America should depart immediately, columnists Rowland Evans and Robert Novak wrote.

Never mind that it was the cutoff of American military aid to South Vietnam — and the Democrats’ refusal to countenance air strikes against the North Vietnamese marauders who were trooping south to stamp out the independence of the Free Vietnamese regime — that had led to the debacle at Saigon. Mr. Biden was among the war critics who favored terminating aid to South Vietnam. He even opposed spending money to aid rescuing our Vietnamese allies.

“I will vote for any amount for getting the Americans out,” Mr. Biden snapped in 1975. “I don’t want it mixed with getting the Vietnamese out.” What would Mr. Biden say, one wonders, to those Vietnamese children, along with the elderly and infirm, who were, as the Vietcong neared, pleading with American troops, climbing over the walls of the embassy at Saigon, clamoring for space on the last Marine helicopters fleeing the doomed capital?

The past was prologue for Mr. Biden as he pushed, as far back as the Obama administration, for America to surrender Afghanistan. Reminded of the likely fate of our Afghan allies, Richard Holbrooke later recounted, Mr. Biden’s reply was “we don’t have to worry about that.” After all, Mr. Biden said, “we did it in Vietnam. Nixon and Kissinger got away with it.” Mr. Biden similarly waved off any concerns over the fate of Afghan women under the Taliban.

“I am not sending my boy back there to risk his life on behalf of women’s rights,” Mr. Biden exclaimed, in Holbrooke’s account. “It just won’t work — that’s not what they’re there for.” It was an echo of Mr. Biden’s dismissive remarks in 1975 about the perils awaiting the Free Vietnamese. “I’m getting sick and tired of hearing about morality, our moral obligation,” he said. “There’s a point where you are incapable of meeting moral obligations that exist worldwide.”

In both cases, America’s moral obligations coincided with our national interest of defending freedom over tyranny, whether communist or Islamist. Mr. Biden’s declaring the Afghan war over doesn’t mean our enemies stopped fighting. Failing to eradicate Al Qaeda and the Taliban there will haunt America for decades — even if Mr. Biden vows that he is “more optimistic about the future” than he was “as a 29-year-old United States Senator.”