The Secretary of Commerce conducts the Census. But he is still bound to follow the law, including the Administrative Procedure Act. That law requires agencies to explain their decisions, to not be arbitrary, and to engage in rational decision-making. They don't get to just lie and fabricate their reasons. Here are the closing lines of the SCOTUS decision: "We do not hold that the agency decision here was substantively invalid. But agencies  must pursue their goals reasonably. Reasoned decisionmaking under the Administrative Procedure Act calls for an explanation for agency action. What was provided here was more of a distraction."