In this particular case, O'Clocksucker didn't change the law; rather, he enforced the law exactly as Congress wrote it, in accordance with his constitutional powers. Roberts et al., is the person who changed the law in order to side-step the 10th Amendment issue by finding that the Act simply does not apply to the type of domestic violence (as in inter-family) at the root of the dispute. In a way, Robert's opinion is an anti-adminstration slap in that the Court essentially found that Holder failed to correctly interpret the law. In contrast, Scalia, Thomas, and Alito found that the Justice Department properly interpreted and applied the law precisely as Congress wrote it; and that the law is unconstitutional under the 10 Amendment as applied to this particular defendant.
Roberts == Screen door [Submarine type].