President Biden proclaimed Thursday, in his first visit to the State Department as president, that “America is back, diplomacy is back.” But something else is back, too: the haunting question of whether the United States can bring the war in Afghanistan, which has vexed the past three administrations, to an acceptable end.

Biden’s speech was his first foreign policy address as president, and he used the opportunity, not surprisingly, to distance himself from his predecessor, Donald Trump. He embraced allies, warned Russia that the days of the United States “rolling over” were finished and offered to work with China even as the two countries compete. He also lauded his audience of diplomats, who had sometimes felt they were on Trump’s enemies list.

Biden seemed to be seeking the same balance on foreign issues he has pursued on domestic policies. He announced a halt to U.S. military support for Saudi Arabia’s war in Yemen, for example, but also said his administration would continue to provide support for the kingdom’s defense. He announced that Tim Lenderking, a respected career diplomat, would be his special envoy for seeking a resolution of the gruesome Yemen war.

Biden didn’t mention what may be the most agonizing foreign policy decision he faces: what to do about Afghanistan, the United States’ longest-running conflict. The intractable, enervating war there is now part of Biden’s portfolio of misery. And over the next few months, he will have to face the hard choice whether to stay or go, this time not as a vice president offering skeptical advice about remaining in Afghanistan but as the ultimate decision-maker.

The Afghanistan dilemma was posed starkly this week in a report issued by a blue-ribbon study group that had been asked to examine strategy for the war by Congress. The panel, co-chaired by retired Gen. Joseph F. Dunford Jr., former chairman of the Joint Chiefs of Staff, urged Biden to abandon Trump’s pledge to withdraw the remaining 2,500 U.S. troops on May 1, as called for in the peace agreement Trump’s envoy, Zalmay Khalilzad, reached with the Taliban in February 2020.

The study group urged Biden instead to hunker down for what could be a protracted effort to negotiate conditions for “an independent, democratic and sovereign Afghan state” — a goal that has eluded the United States and its allies for two decades. Dunford said at a briefing Wednesday that the probability of a civil war in Afghanistan is high if the United States brings home its remaining troops under current conditions.

The real choice facing Biden is “whether to leave or stay for a long time,” argued Carter Malkasian, a former State Department official who is one of the country’s most knowledgeable experts on Afghanistan and was a senior adviser to the study group. He noted that Taliban forces made big gains last year, after the peace agreement, and warned they would take more ground from government forces when the fighting season resumes this spring. “As they make gains, they’re unlikely to compromise,” he said.

“When I look at the costs, leaving now is more compelling than ever before,” argued Malkasian, whose landmark history of the conflict, “The American War in Afghanistan,” will be published in July. He said that to reverse Taliban momentum and restore the stalemate that prevailed when the United States negotiated the peace deal would require substantially more than the 2,500 troops there now or the 4,500 that were on the ground in December.

A similar wary view came from Barnett Rubin, another top expert on Afghanistan who was also a senior adviser to the group. He argued in an interview that it would be a mistake for the United States to unilaterally violate the May 1 departure agreement. Instead, he urged that Biden negotiate a six-month extension, with backing from other countries in the region.

The fact that these two senior advisers expressed concerns about the report’s bottom line illustrates just how delicate the Afghanistan decision will be.

Biden himself has long been a skeptic about Afghanistan. When the military urged a surge in 2009 to combat Taliban gains, Biden was “the only senior official who consistently opposed sending more troops,” wrote Ben Rhodes in his book, “The World As It Is: A Memoir of the Obama White House.” Biden favored a small counterterrorism force and disdained a nation-building role.

But pulling the plug in Afghanistan and admitting defeat after nearly 20 years of fighting would be a bitter pill even for Biden. It would mean a likely civil war, Taliban dominance and probably an eventual reestablishment of al-Qaeda havens as the United States approaches the 20th anniversary of the Sept. 11, 2001, attacks.

Trump left Biden a peace agreement for Afghanistan, and a State Department official said Tuesday that the new administration supports “the ongoing peace process to end the war through a just and durable political settlement.” That’s what the Afghanistan Study Group urged, too.

The problem is that the peace process isn’t working. And Afghanistan is an enduring lesson that in resolving these bitter conflicts, hope is not a strategy.

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