A number of scholars have concluded that there are two cornerstones of the regulatory state:
The Administrative Procedure Act (APA)
Much has been written about centralized regulatory review in recent years and it has been designated at the most significant institutional component of the administrative state. In fact this website is dedicated to that subject; also see theomb.us
With respect to the APA one might designate it as the most significant procedural component of the regulatory state with Senator Norris as its father. Senator Norris introduced S. 1835 in the 73rd Congress (1933), the APA passed in the 79th Congress (1946). Senator Norris, of Nebraska, was Chairman of the Senate Judiciary Committee
See the attached copy of a landmark hearing in the US House of Representatives in 1945. APA History
