KANDAHAR, Afghanistan — Had it not been for dozens of U.S. airstrikes in recent weeks, the southern hub city Kandahar would be under siege, after Taliban fighters threatened to overrun several surrounding districts, security officials say.

Now with President Donald Trump’s orders to cut U.S. forces in Afghanistan by roughly half — from 4,500 to 2,500 — Kandahar’s fate, and the fate of the Afghan security forces spread across the country, are once more in question.

“If it were not for the air support of U.S. forces, the Taliban would be sitting inside Kandahar city now,” Col. Zabiullah Ghorzang, an Afghan army regimental commander, said Tuesday.

The Pentagon on Tuesday formally announced those troop cuts, stopping short of the full withdrawal by Christmas that Trump had mused about publicly and ensuring that the war in Afghanistan will transition to a fourth U.S. administration over almost 20 years of conflict.

The reduction, though expected by Afghan officials, is coming at a desperate time for Afghanistan: Peace negotiations in Qatar between the Afghan government and the insurgency are stalled, Taliban offensives are surging near important cities in the south and north, and morale has been plunging among the Afghan government forces as they take heavy casualties, officials say.

The withdrawal plan has ramifications beyond Afghanistan, including troop cutbacks in the Middle East and Africa.

In Iraq, the American troop presence, which is seen as a hedge against a resurgence of the Islamic State and against powerful Iranian influence, has already come down to about 3,500 troops this year. Under the new orders, Pentagon officials say it will come down to around 2,500 in January. Unlike in Afghanistan, the cuts have not been a source of alarm: Prime Minister Mustafa al-Kadhimi has described the cuts as being agreed to and desirable for both sides.

In Somalia, the withdrawal plan — no formal numbers were announced on Tuesday — is coming as al-Shabab, a terrorist group linked to al-Qaida, continues to intensify its attacks on both military and civilian targets in an effort to topple the country’s Western-backed government.