It began as a righteous cause. It ends with a whimper. By Sept. 11, the 20th anniversary of the attacks that spurred the invasion, U.S. troops will be gone from Afghanistan. So announced President Biden last week.

The American public overwhelmingly supported the decision by President George W. Bush to send troops to Afghanistan. Terrorists using passenger planes and box cutters had brought down the Twin Towers in New York City, symbols of American economic power, and hit the Pentagon, symbol of the nation’s military might. About 3,000 people had been murdered.

The al-Qaida attackers and their leader, Osama bin Laden, had been given protection and a place to train by the Taliban forces that then controlled the country and who shared the same extremist religious ideology and hate for America.

But getting in is always easier than getting out. America’s far superior military power and its professional soldiers quickly expelled the Taliban from control of the central government in Kabul. But through troop surges, withdrawals, and re-surges of U.S. and allied forces, the Taliban and its Pashtun constituency retained control in the rural, mountainous countryside.

The plan was to prop up a strong central government under a constitution. Afghan forces would be trained to secure the country and protect its fledgling democracy so that U.S. forces could eventually withdraw.

But Afghanistan is not a centralized nation. Though it had the manifestations of a functioning government, its authority was largely restricted to Kabul. Corruption remained the primary means to get things done for those sufficiently rich and privileged to afford it. That corruption extended to the military, which might to able to protect Kabul when the Americans leave. Maybe.

President Trump broke with his predecessors’ opposition to direct talks with the Taliban. We don’t negotiate with terrorists, had been the stance. They can talk with the Afghan government. Trump’s change in approach made sense. There could be no peaceful settlement without Taliban buy-in. But the final deal was more U.S. surrender than agreement. It called for a U.S. withdrawal by May 1. Biden, who agreed with Trump on getting U.S. troops home, has only moved the timing.

It is a decision that could lead to some terrible consequences. There are now only about 2,500 U.S. service members in Afghanistan, down from President Obama's 100,000-soldier surge. There was no longer any illusion of “winning” in Afghanistan. But the small force has discouraged the Taliban from trying to seize the central government for fear of inviting a greater U.S. response.

Without any U.S. contingent there, the Afghan government could well fall to the Taliban at some point in the future. That would mean a return to strict Sharia law. There has been impressive progress in educating girls and of women taking positions in government and commerce. That would end and the retaliation would be brutal.

The threat that extremism could take greater hold in neighboring Pakistan, destabilizing an already fragile, nuclear-armed country, would increase as a result of a Taliban-controlled Afghanistan.

The terrorist incubators that America invaded to eradicate at the start of the century could well re-emerge.

In a U.S. preoccupied and divided over domestic issues of ending a pandemic and how, over race relations and the unequal treatment of Black suspects by police, over gun violence and economic inequality — the threat of foreign terrorists has largely receded from the public’s consciousness. Biden’s troop withdrawal was not the issue captivating the public’s attention last week.

But if things go badly, and they may, it could end up being one of his most scrutinized decisions.

The Day editorial board meets with political, business and community leaders to formulate editorial viewpoints. It is composed of President and Publisher Timothy Dwyer, Executive Editor Izaskun E. Larraneta, Owen Poole, copy editor, and Lisa McGinley, retired deputy managing editor. The board operates independently from The Day newsroom.