When the United States dropped the Mother of All Bombs in eastern Afghanistan, it killed scores of Islamist militants, according to officials in Kabul. Here in the U.S., the startled headlines served to remind Americans that their country's longest war continues — and that it has no desirable end in sight.

Are you ready for a second surge in Afghanistan? Gen. John Nicholson, the U.S. commander leading the international forces in Afghanistan, has asked for several thousands more troops to end a stalemate. Afghanistan's foreign minister, Salahuddin Rabbani, has seconded Nicholson's calls.

But it could take much more. A January report from the special inspector general for Afghanistan reconstruction estimated that about 57 percent of the country's districts were in the control of the U.S.-backed government. Roughly a third of the districts were labeled "contested," and about 10 percent were controlled or "influenced" by insurgent groups. That may be an optimistic reading of the situation. Stephen Biddle, who sits on the Council of Foreign Relations, and used to do assessment reports for generals like Stanley McChrystal and David Petreaus, has argued that it could take more than 100,000 U.S. ground troops for America to achieve even the "appearance of victory."

President Trump was always going to face some ugly foreign policy choices in the half dozen or so conflicts he inherited from the two previous administrations. But another surge could end as another farce.

Between Iraq and Afghanistan. U.S. policy has revealed that the primary value of a troop surge is in domestic U.S. politics. For George W. Bush, the troop surge allowed the United States to quell the violence and disorder in the Sunni Triangle long enough for the president to secure the exit of most troops and hand off responsibility to the Iraqi government. The surge worked, in a way, in that it temporarily abated violence, restored some semblance of competence to the presidency, and allowed the war to pass into other hands before the Sunni Triangle erupted again.

In Afghanistan, Barack Obama used a surge of troops to fulfill his campaign promise of focusing on the real war on terror there. His strategy never really developed, however. The surge made the U.S. presence in Afghanistan into the largest counter-terrorism operation in history. But the only way to rout the Taliban was to commit to a sustained counter-insurgency, and perhaps go after America's putative ally Pakistan, which gives shelter to Afghanistan's Islamists. That never happened. Obama got re-elected, and ever since, the story of America's longest war has been the story of American troops exiting the country, Taliban forces regaining larger and larger portions of territory, and the corruption of the American-backed government in Kabul growing.

During his campaign, President Trump asked why America didn't win wars anymore. But he didn't promise an end to the war in Afghanistan. If the U.S. withdraws its remaining 8,000 troops, it will do so knowing full well that the amount of pressure the Taliban can put on the government in Kabul will lead to that government's collapse. That will count as a loss, and it is one that Trump will want to avoid while he seeks foreign policy "wins" in Syria or the Korean peninsula.

The likeliest bet is that Trump will increase troop levels by a small number, perhaps to a point that keeps the risk of a surprise and embarrassment at the hands of the Taliban low. But he will likely hand this conflict to his successor as well. Occasional counter-terror missions and bombing runs will be justified for keeping the Taliban on their toes, and preventing them from launching more complex missions beyond their immediate geographic base in eastern Afghanistan.

In Europe, Japan, and the Korean peninsula, the United States has used troops to keep a long peace going. In Afghanistan, it looks like troops will remain indefinitely to keep America from losing an unwinnable war.