America's Afghan Agony.

Speaking from the White House on Aug. 31, a day after the U.S. concluded its 20-year war in Afghanistan, Pres. Joe Biden declared that our nation needed to rethink its national security strategy. The world is changing," he insisted. Unlike two decades ago, when Al Qaeda operatives crashed hijacked airliners into the World Trade Center and the Pentagon, American defense planning cannot concentrate exclusively on terrorist networks and the states that harbored them. Today's threats differ from those of 2001. Great-power rivalry has returned. 'We're engaged in a serious competition with China," Biden declared, and "dealing with challenges on multiple fronts with Russia."

Biden's attempt to turn the page on the security policy that has guided the nation since the terrorist attacks on New York and Washington, D.C., has been engulfed in criticism. Several critiques stand out. The first questions the decision to withdraw from Afghanistan, arguing that a continuing U.S. military presence coupled with ongoing economic assistance would sustain the Afghan government tang enough for a stable democratic regime to take root.

A democratic Afghanistan, according to this line of reasoning, would deny terrorists sanctuary; therefore, cultivating civil liberties, political competition, and electoral equality in that country is in America's national interest. "The survival of liberty in our land," proclaimed former Pres. George W. Bush in his second inaugural address, "increasingly depends on the success of liberty in other lands."

The principal rebuttal to this argument is that after 20 years of U.S. support at a cost of two trillion dollars, innumerable casualties, and nearly 2,500 American service members' lives, it seems farfetched to imagine that, with just a bit more patience, victory over the Taliban would be achieved and the goal of a unified Afghan democracy realized.

The second prominent criticism of withdrawing from Afghanistan is closely associated with the first. Having sacrificed so much, investing vast resources and incurring irrecoverable costs, the U.S. should stay the course. Opponents dismiss this claim as an example of what economists call the "sunk costs" fallacy. If you find yourself in a hole, they warn, stop digging. The deeper the hole becomes, the more difficult it is to extricate yourself.

Finally, the third major criticism of Biden's policy on Afghanistan concurs with his decision to end the war but blasts its execution. Although it...