If a government official, acting in that capacity, preaches about the Christ, he is clearly breaking the law. If you don't know that, then you should go back to your law school and demand a retroactive failing grade in constitutional law. I'm sure that Everson v. Board of Education, 330 U.S. 1 (1947) was touched on in that class -- when I took a constitutional law class, the professor discussed Justice Black's majority opinion at length.