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WATCH: Steven Cook on Turkey-Russian ties and its effects on NATO

An already-tense relationship between the United States and Turkey got even more contentious after Turkey went through last week with the purchase of a Russian missile defense system known as the S-400, defying U.S. opposition to the deal.

In response, the U.S. booted its NATO ally out of a program that sold F-35 fighter jets to Turkey and trained the country’s pilots. The U.S. maintains that the Russian missile defense system is incompatible with the American jets because they are exactly the sort of stealth aircraft the S-400 is designed to detect.

The dispute has left observers questioning whether Turkey is strengthening its ties with Russia, to the long-term detriment of its NATO partners — a move that could affect U.S. actions in several conflict areas including Syria and Iran.

Steven Cook, a senior fellow for Middle East and Africa studies at the Council on Foreign Relations, joined the PBS NewsHour to explain why Turkey was so set on obtaining the Russian missile defense system, and how it could affect the U.S. and other Western allies.

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