Those efforts failed or fell well short of their aims. Afghanistan remains in the grip of a resolute insurgency and a kleptocratic, dysfunctional governing elite. The Afghan state has been rapidly losing control of districts across the country to Taliban factions and Afghan forces are getting killed and injured at a rate American commanders call unsustainable.

As the Trump administration settles in, American commanders are making the case for another troop surge. Testifying before the Senate last month, Gen. John Nicholson, the current top commander in Afghanistan, said America’s longest war is in a “stalemate” and lamented what he called a “shortfall of a few thousand” troops. There are currently 13,000 international troops in Afghanistan, including about 8,400 Americans. On Thursday, Gen. Joseph Votel, the commander of Centcom, said military leaders are drawing up a new strategy that will require more American troops.

White House officials and members of Congress should consider this request with skepticism. The challenges that have stymied American generals in Afghanistan for years — including havens for insurgents in Pakistan, endemic corruption and poor leadership in the Afghan military — remain unsolved. In the absence of a dramatically different approach to those problems, any new reinforcements can only be expected to shore up the fledgling Afghan government for a year or two.

Sending troops into harm’s way is among the most difficult responsibilities of a commander in chief. Yet there is little evidence that President Trump and his national security team have given the matter substantial consideration since his inauguration. Mr. Trump in 2013 favored a full withdrawal from Afghanistan, calling the war a waste of money. Last year, he said he would stay in Afghanistan, although, he said, “I hate doing it so much.”