If you are wondering how the Congress got away with taking over so much from the state legislatures, you need look no further than Wickard v. Filburn, on which the U.S. Supreme Court unanimously decided that the interstate commerce clause can reach all the way to penalize a farmer for growing his own wheat.
Filburn and his wheat. (Mary Lou Spurgeon NYT)
The complete essay is at Essays on Two Federal Empires.
