Before signing an open letter asking Oprah Winfrey to rescind her endorsement of Jeanine Cummins’ “American Dirt,” her latest book club pick, Jose Antonio Vargas spent the day digging around on YouTube. “I was listening to interviews between Toni Morrison and Oprah Winfrey, and I was listening to them thinking, what would Toni Morrison say about this moment? What would she say to Oprah Winfrey?”