For NATO, Turkey Is a Disruptive Ally

WASHINGTON — When President Recep Tayyip Erdogan of Turkey threatened this month to block NATO membership for Finland and Sweden, Western officials were exasperated — but not shocked.

Within an alliance that operates by consensus, the Turkish strongman has come to be seen as something of a stickup artist. In 2009, he blocked the appointment of a new NATO chief from Denmark, complaining that the country was too tolerant of cartoons of the…