The Supreme Court has been taking advantage of mixed speech—that is, speech that is both private and governmental—to characterize challenged speech in a way that ultimately permits the government to sponsor Christian speech. In Pleasant Grove City v. Summum, a free speech case where the government accepted a Christian Ten Commandments monument but rejected a Summum Seven Aphorisms monument, the Court held that privately donated monuments displayed in public parks were government speech as opposed to private speech and therefore not subject to free speech limits on viewpoint discrimination. In Town of Greece v. Galloway, an establishment case where the local government invited overwhelmingly Christian clergy to give a prayer before town meetings, the Court found no Establishment Clause violation in part by attributing constitutionally troubling aspects of the speech to the private speakers rather than to the government.
Caroline Mala Corbin, Commentary: Exploiting Mixed Speech, 6 Cal. L. Rev. Circuit 37 (2015).