They've been with us a while. For a look at the earlier heritage of this group take a look at a chapter in the book "Since Yesterday" by Frederick Lewis Allen, written very shortly after that decade ended. It had a very interesting chapter titled "They hated Roosevelt". Keep in mind this was written before the great changes bought about with WWII, it was mainly about Roosevelt's campaign and those who 'hated' him. Aside from the usual charges of being a Communist Plant or secretly being a Negro, there were a plethora of other wild theories, like "Eleanor Tuesdays" where supposedly black woman were to shove white women.

I would suggest that this 'style' of hatred in American politics is rooted in the great agrarian/urban shift of the twentieth century as well as the 'end' of the classic "middle vs. coasts" segregation (Midwest and Southerners - largely agricultural, vs. West and East coast industry/trading). The churning factor of modern society broke down doors of relative isolation and lead to vast numbers of people being exposed to - and personally threatened by - vastly different philosophies. That, combined with the vast growth in the executive branch role/power, helped transform the presidency into what seemed a 'crusade', with all its attendant baggage.