NATO Bids From Finland and Sweden Now Depend on Turkey’s President

ISTANBUL—NATO membership for Finland and Sweden, potentially among the most dramatic shifts in European security policy in decades, now depends largely on the decision of one man: Turkey’s President Recep Tayyip Erdogan.

Mr. Erdogan’s decision to block a speedy entrance for the two countries into the North Atlantic Treaty Organization has opened the door to complex negotiations between Western allies and the Turkish government over its stated concerns about the presence of alleged Kurdish militants in Sweden and restrictions on arms sales to Turkey.