[btilly]

That is because Congress has enumerated powers, and the Commerce Clause was then accepted in the intended meaning of only controlling commerce with other countries, between the states, and with Indian tribes. Sales inside of a state are obviously out of the purview of that clause.

Today, of course, the Commerce Clause is interpreted insanely broadly to cover everything from civil rights to environmental protection. Worthy causes, to be sure, but not within the intended purview of, [The Congress shall have Power] To regulate Commerce with foreign Nations, and among the several States, and with the Indian tribes;

[rayiner]

My personal theory of the Commerce Power is that it can be seen as giving the federal government the power to regulate issues that could be described in economic terms as collective action problems. Eliminating infernal tariffs and trade barriers were of course the original animating rationale, but at root that's just one example of a collective action problem. I.e. it makes the country better off not to have internal trade barriers, but states have an incentive to erect trade barriers without some higher authority preventing them from doing so.

While the framers probably didn't fully understand the ramifications, I think the broad language of the Commerce Clause lends itself to a fair reading that Congress can act on matters in which individual states acting alone would face collective action or race to the bottom problems. So something like environmental regulations fits quite naturally into this framework. Pollution doesn't respect state bounderies and states face a race to the bottom problem in attempting to regulate it. Therefore Congress is empowered to act.