Final answer:
The defining point in determining constitutionality in Van Orden v. Perry and McCreary County v. American Civil Liberties Union of Kentucky is the interpretation of the Establishment Clause.
Step-by-step explanation:
The defining point in determining constitutionality in the contemporary cases of Van Orden v. Perry and McCreary County v. American Civil Liberties Union of Kentucky is the interpretation of the Establishment Clause. The Establishment Clause of the First Amendment prohibits the government from endorsing a state-sponsored religion or favoring one set of religious beliefs over others. In these cases, the Supreme Court examined whether government actions, such as displaying religious symbols, violated the Establishment Clause.