In determining whether the activity congress is attempting to regulate has a substantial effect on interstate commerce, reviewing courts typically consider the following factors: (1) whether the regulated activity is commercial or economic in nature; (2) whether an express jurisdictional element is provided in the statute to limit its reach; (3) whether Congress made express findings about the effects of the proscribed activity on interstate commerce; and (4) whether the link between the prohibited activity and the effect on interstate commerce is attenuated.