A broad power to regulate commerce its just one of the things that marks the strength of the federal government. This means that the Congress can impose taxes and fund the military. This was done in response to the Articles of Confederation which did not give these powers to the federal government and thus it was unable to keep the peace and order.
I think you should go with the first one: Because Congress uses a broad definition of the power to regulate commerce, federal power has increased. It caused decreased federal crimes, as it has become easier to define it.
