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When Tony Blair promised in 2001 that Britain would stand by the people of Afghanistan, whom we had helped to liberate from the Taliban, most of us supported him. This newspaper did. The more he said how difficult it might be and that British forces might have to be committed to the mission for some years, the more we were convinced that we owed it to the Afghans to do more than simply install a puppet government, declare the job done and then leave them to the depredations of warlords and Islamist guerrillas.

Not that Hamid Karzai was a stooge of outsiders, of course. He was elected by an emphatic vote in the country's first free and fair elections. He has disappointed some of his own people since then, and he has occasionally offended...