The Istanbul impasse has thus clarified what many in Islamabad have quietly acknowledged for months: Pakistan is effectively done with the Afghan Taliban. Unless a dramatic course correction occurs in Kabul, which seems highly unlikely, the two neighbours are heading toward a prolonged period of cold hostility.

Peace talks in Istanbul between Pakistan and Afghanistan were at a deadlock on Friday, a day after both sides accused each other of mounting border clashes that risked breaching a ceasefire brokered b...