President Donald Trump is arriving in the Turkish capital of Ankara on Tuesday for NATO’s annual summit, where he is expected to pressure the alliance’s members to spend at least 5% of their gross domestic product on defense.

U.S. Ambassador to NATO Matt Whitaker told reporters that “the Ankara Summit will measure the progress” countries have made towards meeting the defense spending threshold. At last year’s retreat in the Hague, the alliance agreed to increase spending from 2% to 5% of GDP under heavy pressure from Trump. Officially, NATO members have until 2035 to reach that goal.