Lepore seems to be making the point that the mob's motivations should have been examined more by the Committee rather than just microfocusing on Trump. My theory is that the mob and the whole Trump movement is an outgrowth of the Industrial Revolution. At its beginning, 70% of the US population lived in the country and 30% lived in cities. A couple of decades later, that percentage was reversed. The 70% of people who have lived in cities for several generations have grown to be a more homogeneous society, much like people in Europe, Japan, or Sweden.
The 30% of people who live in rural places are more diverse but they do share some characteristics. There is less opportunity for them and they feel disenfranchised and disengaged. They feel left out of the mainstream of communication and cut off. These traits would make them more likely to be attracted to leaders who are mavericks. Leaders who can derail the massive influence of the city people. Most of this theory is cobbled together from things I've read, but I've also had many opportunities to get out of the city and mingle with country people and so part of it is from direct observation.