Since this has come up repeatedly in the comments and in discussion about Jeff Sessions citing the Bible as justification for the policy of separating children from their parents, let me make this clear: It is not a violation of the Establishment Clause or separation of church and state for a government official, or anyone else, to offer a religious rationale or argument for or against some public policy.
The policy itself might, if enacted, be constitutionally invalid, but advocating for it is not. So please stop claiming that Sessions citing a Bible verse to support separating children from parents at the border is a violation of separation of church and state. There are lots of other good reasons to criticize him for doing so, but that isn’t one of them.
Separation of church and state does not mean separation of religious belief from political belief. The civil rights movement was based almost entirely in black churches and mosques and Martin Luther King, Malcolm X and many others frequently offered religious arguments in favor of equality. That does not make the Voting Rights Act or the Civil Rights Act unconstitutional, so it certainly can’t make the advocacy of those laws a violation. And we can’t be inconsistent about it and say that it’s a violation when religious arguments are used to justify policies we don’t like, but fine if they are used to justify policies we do like.