Congress can turn all kinds of behavior into crimes. (See State vs. Federal Prosecution.) When Congress does that—when it makes a form of behavior a criminal offense, the offender is subject to prosecution by the federal government. But not all federal statutes reach as broadly as they might appear to. Sometimes, the state is the only one who can punish the behavior in question.
Example: In 1997, the United States ratified the international Convention on Chemical Weapons, whose purpose was to prevent chemical warfare. The next year, in order to implement the convention, Congress enacted a law that prohibits the possession or use of “any chemical weapon.” (18 U. S. C. §229(a)(1).) Federal prosecutors tried to use this law in the case of a woman who spread toxic substances on another woman’s car door, mailbox, and door knob, causing the victim a minor thumb burn. The Supreme Court said that, in order for Congress to regulate “local criminal activity” like this, it has to show that it intended to do so. Otherwise, the activity must be left for punishment under state law. And since the chemical weapon law was designed for chemical warfare rather than simple assault, prosecutors couldn’t use it against the defendant. (Bond v. U.S., 572 U. S. ____ (2014). For more on the case, including the Court’s rationale, see Supreme Court: Why a Love Triangle Isn’t Chemical Warfare.)