Legislation which alters the meaning of the Constitution cannot be said to be enforcing the Constitution. While the line between measures that remedy or prevent unconstitutional actions and measures that make a substantive change in the governing law is not easy to discern, and Congress must have wide latitude in determining where it lies, the distinction exists and must be observed. Congress' discretion is not unlimited, and the courts retain the power, as they have since Marbury v. Madison, to determine if Congress has exceeded its authority under the Constitution.