Back in the 30's the government argued that the grain a farmer produced on his own farm, to feed to his own livestock, precluded him from buying grain from a merchant engaged in interstate commerce of grain and therefore came under the control of the Federal government. If this sounds like a bit of a reach to you, then join the club, however the supreme court agreed with the feds, (Wickard v Filburn) and by extension, the Feds have the right to regulate most of your life.
Commerce is generally described as being an activity involving two or more parties exchanging tangible items of value, or at least promises of items to be delivered later. Minding your own business and NOT buying something from someone in another state, is generally not thought of as commerce, but today, there are new frontiers to be conquered.
In a shocking admission during a federal Court of Appeals hearing on the constitutionality of ObamaCare, attorneys for the federal government asserted in court that the government can force citizens to not only buy health insurance but also other consumer goods such as wheat.Under this logic, if the government decided to "save or create" a bunch of jobs at Government Motors, it could require everyone to go out and purchase a new Chevy. The judges hearing this case were appointed by Obama and Clinton and are expected to rule in favor of the government, which suggests that the case will be decided 5-4 by the US supreme court.