How did Mandelbaum’s nephew Abraham let them down? Maus II

Vladek, Anja, and Mandelbaum meet the smugglers, including the nephew, at the train station, and they all board the train. After about an hour, however, they are arrested and stripped of their possessions. They have been betrayed by the smugglers. Vladek is made to board a truck with a hundred other prisoners and is transported to Auschwitz. Vladek and Anja are separated, not knowing if they will ever see each other again.