The Divider: Trump in the White House, 2017-2021 by Peter Baker and Susan Glasser:
The dispute over Puerto Rico once again demonstrated the limits of Trump’s understanding of the country he governed. When he asked his staff why he should spend so much money on disaster relief there, they had to explain that Puerto Rico was part of the United States.
“They’re American citizens,” Kelly told him.
“They’re not Americans,” Trump insisted.
“Yes, they are,” Kelly replied.