ANKARA, July 4 -- Donald Trump bypassed Congress on June 21 to approve the sale of $700 million in General Electric F110 jet engines to Turkey. It was the kind of decision that ends careers for the officials who sign off on it, and Trump made it thirteen days before the NATO summit in Ankara. Every alliance member understood what it meant.

Recep Tayyip Erdogan enters next week's summit in a position no Turkish president has occupied in more than a decade. Trump needs him. The question now circulating in NATO capitals is what Erdogan intends to collect on that debt, and whether the alliance can accommodate his terms without breaking what little cohesion it still has.

The summit is scheduled for July 7 and 8. Ankara is hosting, unusual in...