Congress may regulate interstate channels, instrumentalities and persons or things in commerce, and economic activity with a substantial relation to interstate commerce. The aggregation principle can reach local economic conduct whose class has a substantial interstate effect.

Limits matter. In United States v. Lopez, the Court rejected a federal gun-possession law whose regulated activity was neither economic nor adequately connected to commerce. The decision did not return commerce doctrine to a narrow border-crossing rule; it required a judicially enforceable connection to an enumerated power.

Identify the regulated conduct, not merely the policy's national importance. A commercial transaction, transportation network, or economic production rule presents a stronger commerce link than an ordinary local crime. Valid commerce legislation can preempt state law, but congressional purpose cannot cure a missing constitutional basis.

Video lesson: Congressional Decisions: Crash Course Government and Politics #10