“So I'm a Mexican American from a poor, rural (mostly white) town in Oklahoma. Missing from this debate? How poor whites see themselves.” They don't see themselves as poor. They don't base their identity on it. They see themselves as "temporarily embarrassed millionaires."
The middle class, which Pew defines as two-thirds to two times the national median income for a given household size, began to grow after World War II due to a surge in economic growth and because President Franklin Delano Roosevelt’s New Deal gave workers more power. Before that, most Americans were poor or nearly so.