This may be a bit lowbrow, but I've been flipping through cable and stumbled across a History Channel piece on the history of crime, which put its hook in me and I watched for a while. One of the points made in its coverage of crime in the summer of 1933, during the Great Depression, was that local law enforcement quickly became incapable of fighting back against increasingly better armed gangsters.
Small towns were selected principally due to their inability to protect themselves. Many of the names were familiar with during this time (Dillinger, Bonnie and Clyde, etc...) were in operation at the same time period, which caught the attention of the national media. For an ambitious bureaucrat like J. Edgar Hoover this was a perfect opportunity to expand his institution's authority. Though law enforcement had previously been primarily a state and local domain - a reserved power - support increased for the national involvement in order to assist local authorities, and the increased focus on criminality led to popular support. Since banks had been robbed, and the crimes crossed state borders, the constitution's commerce clause was used as providing justification for the expansion of power.
The point I'm making is that quite often when people discuss constitutional issues, especially those involving expansions of national power, we tend to only focus on the textbook problems associated with how terminology is interpreted and forget about the pragmatic problems faced at different points in our history and how expansions of national authority were considered to have been practical solutions to those problems.
File this under ideology versus pragmatism.
