When the great Italian conductor was dissatisfied with an orchestra’s performance, Terry Teachout writes, “he flew into screaming rages whose verbal violence would likely not be believed were it not for the fact that there were secret tapes made.” As far as his private life was concerned, he was “a compulsive philanderer whose love letters to his mistresses are explicit to the point of pornography.” Yet, as a new biography shows, he displayed a great deal of moral integrity when he was wooed by murderous regimes:
[T]here is . . . a parallel between the passionate conscientiousness of [Toscanini’s] music-making and his refusal to compromise with Hitler and Mussolini, both of whom were sufficiently knowledgeable about music to understand what a coup it would have been to co-opt the world’s greatest conductor. . . .
If anything, Toscanini’s hatred for the Nazis was even more potent [than for Italian fascists], above all because he was disgusted by their anti-Semitism. A philo-Semite who referred to the Jews as “this marvelous people persecuted by the modern Nero,” he wrote a letter to one of his mistresses in the immediate wake of the  Anschluss [of Austria] that makes for arresting reading eight decades later, “My heart is torn in bits and pieces. When you think about this tragic destruction of the Jewish population of Austria, it makes your blood turn cold.” . . .
Toscanini felt so strongly about the rising tide of anti-Semitism that he agreed in 1936 to conduct the inaugural concerts of the Palestine Symphony (later the Israel Philharmonic) as a gesture of solidarity with the Jews. In an even more consequential gesture, he had already terminated his relationship with the Bayreuth [music] festival, where he had conducted in 1930 and 1931—the first non-German conductor to do so. While the founder of the festival, Richard Wagner, ranked alongside Beethoven, Brahms, and Verdi at the top of Toscanini’s pantheon of musical gods, he was well aware that many of the members of the Wagner family who ran Bayreuth were close friends of Adolf Hitler, and he decided to stop conducting in Germany—Bayreuth included—when the Nazis came to power. . . .
Toscanini never performed in Germany again, nor would he forgive those musicians . . . who continued to do so.