54. What constitutional provision would be most helpful to the principal's defense?

C is correct. Article I, Section 10 of the Constitution prohibits states from passing ex post facto laws. An ex post facto law punishes conduct that occurred before the law became effective. Because the principal had enrolled the foreign nationals before the state adopted the law under which he was prosecuted, it was an unconstitutional ex post facto law as applied to his prosecution.

A is incorrect. Although the state law deprives the principal of his freedom to enroll foreign nationals in his school, this liberty interest is not fundamental. A court therefore might well reject a due process challenge to the state's application of the law to the principal on the ground that the application is rationally related to a legitimate government interest.

B is incorrect. Although the state law classifies state employees who provide the prohibited services and subjects them to a special penalty, the classification is not constitutionally suspect, nor does it burden a fundamental individual right. A court would thus reject an equal protection challenge to the state's application of the law to the principal because the classification is rationally related to a legitimate government interest.

D is incorrect. U.S. Supreme Court precedent limits the protections of the Privileges or Immunities Clause of the Fourteenth Amendment to a handful of rights specifically associated with national citizenship, none of which are applicable in this case.