Complex sentence: During his time there, Flexner helped to bring over many European scientists who would have likely suffered prosecution at the hands of the rising Nazi government, including penning the letter inviting Albert Einstein to the Institute and to the United States.
Split into simpler sentences: During his time there, Flexner helped to bring over many European scientists who would have likely suffered prosecution at the hands of the rising Nazi government. Flexner even penned the letter inviting Albert Einstein to the Institute and to the United States.