Also, there just weren't many Federal criminal laws until the late 19th century and especially early 20th century. What preceded and ushered in the so-called ad

Also, there just weren't many Federal criminal laws until the late 19th century and especially early 20th century. What preceded and ushered in the so-called administrative state and expansive Commerce Clause powers was the emergence of Federal morality laws, such as the 1895 Federal Lottery Act[1] and the 1910 Mann Act.[2] Excepting brief periods during the Civil War and Reconstruction, Federal crimes only pertained to very specific areas under Federal jurisdiction, such as acts on federal property, violations of Federal tax laws (e.g. import/export), etc, none of which required an extensive, general purpose investigatory and enforcement apparatus. There were Federal agencies that performed investigations, of course, most famously the Federal Marshal Service and Secret Service. The power to investigate and enforce was always concomitant with the power to legislate, and naturally followed the enactment of such legislation. [1] See https://en.wikipedia.org/wiki/Champion_v._Ames https://en.wikipedia.org/wiki/Champion_v._Ames [2] Supreme Court precedents applying these two acts is what opened the door to predominantly intra-state activity being captured by Federal inter-state powers.