Final answer:
The grandson of P.B.S. Pinchback is not mentioned in the reference materials provided, suggesting a potential research error as Pinchback's family does not appear in prominent roles during the Reconstruction era. It could involve a lesser-known relative or incorrect information.
Step-by-step explanation:
The question refers to the powerful political career of a grandson of P.B.S. Pinchback during the Reconstruction era. Pinchback served as the first African American governor of a U.S. state (Louisiana) and was a significant figure in the Reconstruction era politics. Reconstruction was the period following the Civil War when the United States endeavored to reintegrate the former Confederate states and newly freed slaves into the country. This era saw many African Americans like Hiram Revels and Blanche K. Bruce serve in the United States Senate and others in various levels of government. However, there isn't a direct reference in the provided material that mentions the grandson of P.B.S. Pinchback having a powerful political career, suggesting that this might be a research error. Moreover, it could potentially refer to a lesser-known relative whose political role wasn’t as prominently recorded in historical texts provided or is beyond the knowledge cutoff date.