8 On the other hand, those ecclesiastical authorities should realize that the rulers of the state can and ought to trust them; nor should the ecclesiastical rulers accept a cause, such as retaining laws, which the interests of the Church do not want retained. Suspicion and lack of trust often result from the rivalry of political parties. This you know well from experience. Surely the greatest duty of Catholic men and especially of clerics is never to support a cause or to offer an opinion if it conflicts with the faith of the Church or counteracts the preservation of its rights. Everyone may hold his own opinion in purely political matters and defend it honestly and legitimately, provided it is not contrary to religion or justice. Yet those, if there are any, who do not distinguish clearly between what is holy and what is merely civil, commit a pernicious error which lends the name of religion to a political party.
Source: Pergrata (Vatican.va)