The challenges awaiting Trump at the NATO Summit, taking place Tuesday and Wednesday at the Presidential Complex in Ankara, will be far more difficult. In the Turkish capital, he will confront two major crises—Iran and Ukraine—while also managing increasingly complicated relations with allies who did not support him during the recent war with Iran. Trump has warned that he could treat those allies similarly if they seek U.S. assistance in the future and may even take the additional step of beginning to withdraw American forces from Europe.