The biggest problem with Christian Nationalism is that the term is so broad as to mean just about anything.

As for school choice, yes, parents should be allowed to use the vouchers for religious schools.

Amendment I

Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the Government for a redress of grievances.

Secularists are so arrogant in this matter. They think their worldview is the only acceptable worldview and want their religion to be the official state religion. There is nothing neutral about their worldview.