commerce clause
Article I, Section 8, paragraph 3 gives Congress authority "To regulate Commerce ... among the several States ...." In other words, the Founders intended the federal government to oversee the original North American Free Trade Zone. It would make little sense for independent states not to be able to trade with one another (protectionist trade barriers had been common among States).
Reference
Walter E. Williams. I'll quote the relevant excerpts here:
As James Madison, the father of our Constitution, explained, "The powers delegated by the proposed Constitution to the federal government are few and defined. Those which are to remain in the State governments are numerous and indefinite."
The ninth and tenth Amendments served their intended purpose for many decades, until finally, about the 1930s, the courts began to cave.
That tyranny was sealed in 1942, by a little known U.S. Supreme ruling in Wickard vs. Filburn.
Filburn was a small farmer in Ohio. The Department of Agriculture had set production quotas. Filburn harvested nearly 12 acres of wheat above his government allotment. He argued that the excess wheat was unrelated to commerce since he grew it for his own use. He was fined anyway. The court reasoned that had he not grown the extra wheat he would have had to purchase wheat -- therefore, he was indirectly affecting interstate commerce.
In other words, Filburn was fined not for something he did, but for something
he didn't do, that could have, in some imaginable way, affect interstate commerce!
It was on that date I imagine the Founders collectively rolled in their graves.
Why is this gun-related you ask. I'm glad you asked.
In 1990 the US passed the Gun-Free School Zones Act,
citing its powers under the Commerce Clause! Namely, the possession of a firearm in a local school zone substantially affected interstate commerce.
Huh???
Violent crime raises insurance costs, and those costs are spread throughout the population. Violent crime reduces the willingness of individuals to travel to high-crime areas within the country. Finally, crime threatens the learning environment, thereby reducing national productivity.
Yes this is a glimpse into the the cogitations of some of your favorite elected representatives. Scary, no? It is a similar interpretation that requires you to pay Social Security taxes. You can't, for instance, opt out of paying Soc Sec since you might someday take your accumulated earnings and spend them in a state where you didn't earn them. THe commerce clause, again.
Back to Gun-Free Schools. As you are aware SCOTUS overturned the Gun-Free School Zones Act in 1995 saying,
If we were to accept the government's arguments, we are hard pressed to posit any activity by an individual that Congress is without power to regulate.
No kidding!
So: cooler heads did eventually prevail. As they may again if SCOTUS decides to hear the Heller vs. DC case. The outcome of that decision may answer your question more directly.