Friend Miles Smith posted his comments on "White Trash" here. I am a bit less sanguine. Nonetheless, I can report without hesitation that Isenberg has performed a valuable service by telling the largely untold story of how many of the English who first came to America were from the very bottom of English society, sent to the Colonies for expediency's sake. In other words, through the first decades of the 17th century, untold thousands came to America not to make a new life for themselves nor to practice their religion free of England's established church. Rather they came as England's "offscourings," sent as indentured servants or with only the barest evidence of consent.
As such, the Colonies' initial lower class frequently died from their lack of even basic life-skills. They didn't know how to farm because over a century earlier the English land magnates had enclosed their estates, sending peasants with only copy-hold interests to fend for themselves as beggars or to seek employment in England's nascent industries or to be dragooned into military service. You can read something of of the effects of enclosures on the common law of contracts and how it was decried (long after the fact) in the Westminster Larger Catechism in my article, The Puritan Revolution and the Law of Contracts (download here or here).
Thus begins Isenberg's account of America's permanent white underclass. Isenberg fast forwards to the post-Independence period where she contrasts the opinions of Benjamin Franklin and Thomas Jefferson on what to do with this underclass. As with England's pushing its underclass to the Colonies, American leaders in the late 18th century wanted this class to go west, to the unsettled lands of the opening Northwest and Southwest Territories. Remarkable, the terms of opprobrium used with respect to this class differed little from over a century earlier. The contempt of the elites and middle classes for the shiftless and feckless underclass was pervasive and few thought that many from this group could be salvaged. They were good for little more than clearing the Natives from unsettled areas only to be evicted themselves because they didn't have good title to their newly settled lands.
With the broadening of the franchise in the early nineteenth century, Isenberg portrays how even Andrew Jackson, the hero of the common man, had little affection for the deep underclass. Both Jackson and his political enemy Henry Clay could appeal for their votes while supporting the claims of land speculators over squatters in fights over title to the land. Writers in the nineteenth century for the first time, however, sometimes portrayed those now known as crackers in a sympathetic light. Such sympathies largely disappear with the advent of the Civil War when the Southern elites co-opted (or drafted) support from the large numbers of tenant farmers by appealing, on the one hand, to their fear of Black emancipation and, on the other, to their shared contempt for Northern mudsills, and were not to return until the Great Depression.
I will fast forward to the final chapters of "White Trash" where Isenberg's touch with her accumulations of social and cultural data becomes less deft. By the middle of the 1960's, with the programs of FDR's New Deal and LBJ's Great Society, the poor white underclass had become the object of sustained federal attention. By the 1970's, a certain hillbilly chic had developed. Concurrently with the rise of tributes to good 'ole boys and NASCAR was the film Deliverance, which portrayed backwoods rednecks in an extraordinarily vile light. What accounted for cracker pride and simultaneous cultural contempt? Isenberg can't quite say but argues that a substantial white underclass remains and will remain unless addressed by massive governmental intervention.
In short (which is tough for a book of 321 pages (and 123 more pages of endnotes)), Isenberg argues that America has been and is still a society stratified by class as much as race, and that America has and continues to deny the existence of class. And, notwithstanding the vaunted American Dream, upward mobility is uncommon; what predicts childrens' success is their parents class.