Turkish President Recep Tayyip Erdoğan’s determination to purchase Russian anti-aircraft missile systems could cripple his country’s participation in the NATO alliance, Vice President Mike Pence warned Wednesday.

“Turkey must choose: Does it want to remain a critical partner of the most successful military alliance in the history of the world?” Pence said at NATO Engages, an event hosted on the sidelines of the NATO summit in Washington. “Or, does it want to risk the security of that partnership by making reckless decisions that undermine that alliance?”