Afghan security forces inspect a vehicle damaged by rocket fire in Kabul, Afghanistan, July 20.

Afghan security forces inspect a vehicle damaged by rocket fire in Kabul, Afghanistan, July 20.

Photo: Anadolu Agency via Getty Images

The situation in Afghanistan is deteriorating rapidly. As the U.S. and its international partners withdrew military forces over the past few months, the Taliban roughly tripled the territory under its control. If the U.S. and allies don’t take urgent action, the world will bear witness to a disaster.

The Taliban and its allies have taken control of more than 145 districts over the past two months, according to Foundation for Defense of Democracies analysts. The Taliban now threaten half of Afghanistan’s provincial capitals. The Taliban offensive in the north is particularly consequential because it is designed to strike the Afghan government’s power base and pre-empt the reconstitution of an anti-Taliban “northern alliance.” The point is clear: The Taliban intends to isolate and overthrow the government in Kabul.

An American priority must be preventing the collapse of the Afghan government, lest the Taliban’s partners, including al Qaeda and other jihadist terrorists, re-establish a base to plan, prepare and direct attacks against the U.S., its allies and others who don’t conform to their perverted interpretation of Islam. Other objectives should include limiting the humanitarian disaster and ensuring that the gains the Afghan people—especially women and girls—made since 2001 aren’t lost.

Failing to help Afghans who reject the Taliban’s advocacy of hatred and violence would lead to an unmanageable refugee crisis, which would destabilize Afghanistan’s nuclear-armed neighbor, Pakistan. Refugees would continue their journey beyond Central and South Asia to Europe and beyond.

Pointing out the dire situation in Afghanistan and the threat it presents to American interests isn’t intended to relitigate President Joe Biden’s April 14 decision to withdraw. But the conditions in Afghanistan expose the flawed assumptions and self-delusion on which that decision was based. Reality demands a new set of actions to protect American security and humanitarian interests.

As a first step, the U.S. should station close air support assets in Afghanistan and make clear that America will provide air support to Afghan forces. By ending almost all U.S. air support, America has enabled the Taliban’s extraordinary gains and reduced the morale of Afghan partners who had already been bearing the brunt of the fight. Many Afghans were willing to fight and die—tens of thousands have made the ultimate sacrifice since 2001—on the assumption that support from the air was available when needed. The sudden end of that support demoralized many Afghan forces while encouraging the Taliban.

American air assets in Afghanistan should help Afghan forces defend Kabul and provincial capitals, as well as attack Taliban forces that target Afghan civilians or attempt to fire their newly captured artillery into population centers.

Some may cite the 2020 U.S.-Taliban agreement as a reason not to take this step. But the Taliban never honored the agreement, continuing to work closely with al Qaeda and intensifying murderous attacks on Afghan civilians. Why should the U.S. adhere to an agreement that the other party has abrogated?

As a second step, the U.S. and its allies should ensure the Afghan Air Force has comprehensive contractor maintenance and logistics support based in Afghanistan. The Afghan Air Force provides Kabul a major advantage over an enemy whose principal tactic is murdering civilians. Afghan-provided close air support, air resupply and medical evacuation are possible only with well-maintained fixed and rotary wing aircraft.

Third, the U.S. and partners should provide Afghan security forces with extensive intelligence, surveillance and reconnaissance support. The Taliban are trying to stretch the Afghan military by forcing them to defend everywhere. Giving Afghan leaders a heads up about Taliban activities can help the Afghans to concentrate force against the enemy.

Finally, Washington should stop advocating actions that strengthen the Taliban and weaken the Afghan government and security forces. For example, responding to pressure from Washington, the Afghan government released 5,000 prisoners in accordance with the 2020 agreement. Many of them belonged to al Qaeda.

Additional releases would give the Taliban and al Qaeda more manpower. It is important to remember that in 2011 released al Qaeda in Iraq terrorists helped establish Islamic State. After Islamic State gained control of territory the size of Britain, U.S. and allied forces deployed to Iraq and Syria to halt the humanitarian disaster, regain control of territory, and ensure the enduring defeat of what had become the most destructive terrorist organization in history.

These actions may be insufficient to arrest the Taliban’s brutal offensive. But without them, what’s likely to come is a collapse in Afghanistan that will embolden the enemies of all civilized peoples and compel a much more costly intervention later.

Mr. McMaster, a retired U.S. Army lieutenant general, served as White House national security adviser, 2017-18. He is a senior fellow at the Hoover Institution and chairman of the Center on Military and Political Power at the Foundation for Defense of Democracies. Mr. Bowman is the center’s senior director.

As the U.S. continues its troop withdrawal from Afghanistan ahead of President Biden’s Sept. 11 deadline, the Taliban is rapidly advancing around the country. Image: Reuters The Wall Street Journal Interactive Edition