Here goes the super short version, Laura. Hoffer’s book, The True Believer, deals with the psychology of mass movements in religion and politics and combinations of both. When he writes of the new poor he see them as one of the biggest destabilizing forces of a society. You see the chronically poor, having never known good times are pretty much content with their lot in life, but not the new poor. With them the loss of good times is still fresh in mind and it eats at them.
In America the new poor would be those folks of modest education who enjoyed relatively high paying factory jobs between, say, 1950 and 1975, and all the way to around 2000 in some cases. Once these jobs dried up because of technology or were shipped overseas, a whole class of disgruntled new poor was created. It was this class of new poor that Trump targeted to become president.