For me it's the separation of church and state: in 2 parts

Part 1

Again, the Johnson Amendment gets to the heart of ensuring the First Amendment. What if a religious candidate proclaimed that if elected, he would do his utmost to outlaw all birth control drugs and devices, “because the bible tells me to do so.” If so, then that person should not hold public office in the United States. Not because of a “religious test” against that candidate because of his fundamentalist faith, but rather because of his attempt to “establish” religion as the ultimate source and sanction of secular U.S. law (contrary to the First Amendment to the Constitution) and to impose his religious beliefs upon citizens that do not share these beliefs.