31 From God has the duty been assigned to the Church not only to interpose resistance, if at any time the State rule should run counter to religion, but, further, to make a strong endeavor that the power of the Gospel may pervade the law and institutions of the nations. And inasmuch as the destiny of the State depends mainly on the disposition of those who are at the head of affairs, it follows that the Church cannot give countenance or favor to those whom she knows to be imbued with a spirit of hostility to her; who refuse openly to respect her rights; who make it their aim and purpose to tear asunder the alliance that should, by the very nature of things, connect the interests of religion with those of the State. On the contrary, she is (as she is bound to be) the upholder of those who are themselves imbued with the right way of thinking as to the relations between Church and State, and who strive to make them work in perfect accord for the common good. These precepts contain the abiding principle by which every Catholic should shape his conduct in regard to public life. In short, where the Church does not forbid taking part in public affairs, it is fit and proper to give support to men of acknowledged worth, and who pledge themselves to deserve well in the Catholic cause, and on no account may it be allowed to prefer to them any such individuals as are hostile to religion.
Source: Sapientiae Christianae (Vatican.va)