In the Garden of Beasts by Erik Larson

This book is subtitled 'Love, Terror and an American Family in Hitler's Germany' and is about the US Ambassador to Germany immediately before WWII started, beginning in 1933 until 1938.
William Dodd (no relation to Thomas Dodd, a judge at Nuremberg after WWII) was a college professor, and not a very happy one. He was looking for something else to do. President Roosevelt had a big problem--no one with any kind of political savvy wanted to be the US Ambassador to Germany, seeing the handwriting on the wall--that that was literally a dead end political job, a no-win situation. So Roosevelt tapped Dodd for the job--as a non-politician he really had no idea what he was getting into, and he spoke fluent German, so off he went to a job no one wanted.
His family socialized with Nazis and advocated for them back in the US, despite a growing body of evidence that all was not going well with Germany if you were at all tolerant. People were being abducted and murdered, and the lack of tolerance of any differences was becoming, well, intolerable. It took Dodd a long time to say that enough was enough and come home, and this book is the story of what happened leading up to his departure.