 Ankara purchased a Russian-made missile system, despite NATO objections that it would allow Russian intelligence to harvest information. In retaliation, NATO expelled Turkey from the alliance's program to build F-35 fighter jets. Turkish officials say they're still waiting on a refund. Then, after the invasion of Ukraine, Turkish leader Recep Tayyip Erdogan stalled the entry of new members Sweden and Finland for almost two years over objections to their policies towards the PKK.