I think this document called *The Participaton of Catholics in Political Life *addresses your question directly. I would argue that Catholics do have an obligation to resist in the temporal order (i.e., politics) that which contradicts or offends the moral order. Emphasis mine:
[quote=]By fulfilling their civic duties, “guided by a Christian conscience”, in conformity with its values, the lay faithful exercise their proper task of infusing the temporal order with Christian values, all the while respecting the nature and rightful autonomy of that order, and cooperating with other citizens according to their particular competence and responsibility. The consequence of this fundamental teaching of the Second Vatican Council is that “the lay faithful are never to relinquish their participation in ‘public life’, that is, in the many different economic, social, legislative, administrative and cultural areas, which are intended to promote organically and institutionally the common good”. This would include the promotion and defence of goods such as public order and peace, freedom and equality, respect for human life and for the environment, justice and solidarity.
[quote=]When political activity comes up against moral principles that do not admit of exception, compromise or derogation, the Catholic commitment becomes more evident and laden with responsibility. In the face of fundamental and inalienable ethical demands, Christians must recognize that what is at stake is the essence of the moral law, which concerns the integral good of the human person. This is the case with laws concerning abortion and euthanasia (not to be confused with the decision to forgo extraordinary treatments, which is morally legitimate). Such laws must defend the basic right to life from conception to natural death. In the same way, it is necessary to recall the duty to respect and protect the rights of the human embryo. Analogously, the family needs to be safeguarded and promoted, based on monogamous marriage between a man and a woman, and protected in its unity and stability in the face of modern laws on divorce: in no way can other forms of cohabitation be placed on the same level as marriage, nor can they receive legal recognition as such.