  Following the identification of the pairing state, the major challenge in
understanding the cuprate superconductors has been determining the evolution
with doping and temperature of their anomalous normal state behavior. Key to
this understanding is the experimentally determined magnetic phase diagram for
the cuprates, which provides information on the protected magnetic properties
of the normal state, generic behavior that is reliably the same one system to
the next, regardless of details. I discuss the constraints this places on
candidate quantum protectorates, and the status of microscopic model
calculations for a protectorate consistent with these constraints, the nearly
antiferromagnetic Fermi liquid.
