However, the Nazi regime sought to suppress any source of ideology other than its own, and set out to muzzle or crush the churches in the so-called Kirchenkampf. When Church leaders (clergy) voiced their misgiving about the euthanasia program and Nazi racial policies, Hitler intimated that he considered them "traitors to the people" and went so far as to call them "the destroyers of Germany".[43] The extreme anti-Semitism and neo-Pagan heresies of the Nazis caused some Christians to outright resist,[44] and Pope Pius XI to issue the encyclical Mit Brennender Sorge denouncing Nazism and warning Catholics against joining or supporting the Party.