To a great extent, Roy Cohn's power shift is significant because it connects to the basic theme of change and transformation that Kushner feels is intrinsic to what it means to be both a human being and what it means to live in America.  Cohn believes that his being of power and political machination is what defines reality.  However, these elements of temporal control cannot offset the seismic change both he and his vision of America undergo.  His love of power does not protect him from the disease ravaging his body and from facing the ghosts of his past, particularly in the form of Ethel Rosenberg.  His vision of America is not going to remain intact, as the fall of the Soviet Union will bring with it a challenge to the overall premise of the Conservative vision that the Soviet Union is the embodiment of evil.  The power shift that Roy undergoes from one of power and control to a condition of being disenfranchised by a disease that was not understood and actually demonized by the very same system and people that Roy covets is part of this transformation process.  Power and control are temporal conditions, constantly shifting as no different that the Continental principalities that are always subject to plate tectonics and the mere element of being in the world.  In this, Roy is no different than any other being and is governed no differently by the same forces that initiate change and the life force that defines and is intrinsic to human consciousness and the same zeitgeist that defines and is intrinsic to America.