The election of Donald Trump as the 45th President of the United States meant that the American people for the first time in 70 years elected a president who was against transatlantic cooperation including the cooperation on security within the framework of NATO. During his first 30 months in office, Donald Trump kept a remarkable number of the foreign policy promises he issued during the election campaign in 2016. It is surprising that the president did not take drastic steps toward the American commitment to NATO. The chapter asks why there was this disconnect between words and deeds when it came to transatlantic cooperation on security. It is the argument of the chapter that a number of domestic circumstances contribute to explaining the puzzling lack of coherent action by Donald Trump when it comes to NATO. The combination of three domestic variables, the crucial position of NATO within American strategic culture, a favorable public opinion and clear signals from Congress, has been capable of restraining the impact of an impulsive and unpredictable president. It explains why the United States remains in the NATO in spite of Donald Trump’s heavy attacks on the European partners.