THIS week General John Nicholson, the commander of America’s forces in Afghanistan, completed a review of what will be needed to contain the growing insurgent threat posed by the Taliban and its allies. After reading his recommendations, Barack Obama will have to make a decision he surely hoped to pass on to the next president: whether to ramp up American troop numbers in Afghanistan again. General Nicholson has probably asked Mr Obama at least to halt his planned reduction of America’s troop levels from 9,800 to 5,500 by the end of the year. Mr Obama has often seemed to think he could end the war in Afghanistan simply by declaring it over. But the enemy has not co-operated. Afghan forces have fought bravely since the end of 2014, when NATO combat troops formally left. But they were not ready to cope with the sudden departure of their allies, while the Taliban remained resilient and capable.

The Afghans are suffering losses that American commanders warn are unsustainable (see table). Not since 2001 have the Taliban held as much territory as they now do. Civilian casualties are mounting, as Afghan soldiers have been stretched thin across multiple fronts. Michael O’Hanlon of the Brookings Institution, a think-tank, says that the loss of American air power has particularly hampered the Afghan army’s ability to carry out attacks: units in trouble can no longer call in reinforcements or air strikes.

Even current troop levels—6,954 Americans to train and help Afghan forces and 2,850 on separate counter-terrorism missions, with NATO contributing a further 5,859 soldiers—appear inadequate. Mr Obama’s administration understands this, at least tacitly. The House Armed Services Committee recently revealed that 26,000 military contractors are in Afghanistan—an unusually high number. They do a lot of jobs that troops would normally do, allowing Mr Obama to hold the headline figure for troops deployed below 10,000.

Nor is it just a question of numbers: what the White House lets its soldiers do also matters. American special forces go discreetly into action with their Afghan counterparts. But most troops in the “train and assist” mission are not embedded with Afghan combat units, where they would be in harm’s way but also of most practical help.

Restrictions on air power are even more frustrating for field commanders. American combat aircraft may only be used against designated terrorist groups, such as al-Qaeda and Islamic State, or when either NATO troops are imperilled or “strategic collapse is imminent” (for example, if a big city is about to be captured).

Few can see the sense of this. David Petraeus, a former commander in Afghanistan, and Mr O’Hanlon recently urged Mr Obama to change the rules of engagement. They pointed out that America is dropping and firing 20 times more bombs and missiles in Iraq and Syria (neither especially intense air campaigns) than in Afghanistan. Anthony Cordesman of the Centre for Strategic and International Studies says that “US and allied air power is critical” to prevent the Afghan army’s defeat.

To bolster his case, General Nicholson points to “overt cooperation between the Taliban and designated terrorist organisations”. He fears that if the Taliban returned to power in some parts of the country, “they would offer sanctuary to these groups.” He already has the bipartisan support of 10 of the 26 members of the Senate Armed Services Committee, who wrote to Mr Obama on May 26th urging him to give General Nicholson’s advice “extraordinary weight”. On June 3rd, 13 senior diplomats and retired generals, who oversaw military operations and policy in Afghanistan under both the Bush and Obama administrations, sent the president an open letter calling on him to maintain current force levels.

Whatever Mr Obama decides, his successor will still have to make some difficult choices. It would be better if those choices were informed by sober realism rather than wishful thinking.