Turkey has become a real thorn in the side of NATO, as The National Interest explains to readers:
It was 2004, and the geopolitical chess pieces were positioned very differently from how they are today. Back then, Turkey wanted to join the European Union, Great Britain thought that that was a magnificent idea and France was skeptical. Oddest of all, the most vocal advocacy for Turkish accession and democratic reform came from an unlikely alliance of then-president George W. Bush and then-prime minister Recep Tayyip Erdogan.
Two years later, he was even more explicit, asserting in Istanbul that “as a European power, Turkey belongs in the European Union.”
Alas, a lot changed 2004: the Iraq war went south, Syria was immersed in chaos, refugees flooded into Europe, Germany throttled Greece with failed economic reforms, discontent with the EU spread, Britain voted for Brexit, Erdogan took a sudden dictatorial plunge and tens of thousands in Turkey were detained after a coup attempt. Bush’s idealistic hopes were crashed on the shoals of reality.
Turkey once sought to meet EU standards, today the EU is scrambling to appease Turkey so an agreement on the migrant crisis doesn’t get scrapped. Ankara is threatening to pull out of talks unless it’s granted visa-free travel within the Schengen Area—which would play into the hands of European nationalists, which could weaken the EU even further. Turkish membership has also grown unpopular; in Britain, it was a potent issue for the successful Leave campaign.