We encourage all citizens, particularly Catholics, to embrace their citizenship not merely as a duty and privilege, but as an opportunity meaningfully to participate in building the culture of life. . . . Every act of responsible citizenship is an exercise of significant individual power. We must exercise that power in ways that defend human life, especially those of God's children who are unborn, disabled or otherwise vulnerable. We get the public officials we deserve. Their virtue–or lack thereof–is a judgment not only on them, but on us. Because of this we urge our fellow citizens to see beyond party politics, to analyze campaign rhetoric critically and to choose their political leaders according to principle, not party affiliation or mere self-interest.

 -- Living the Gospel of Life: A Challenge to American Catholics, 34,
National Conference of Catholic Bishops, November 1998

The first principle of morality is to do good and avoid evil. We cannot really do this unless we know what good things ought to be sought, and what evils are to be avoided entirely, or tolerated for a time under certain circumstances. In all of this Catholic teaching gives us concrete guidance.

This obligation flows from the virtue of faith, since belief in Christ is also belief in the Church and Christ’s promises to the Church.

We are morally obliged to perform acts which are good

Prudence is the Queen of Virtues, as it governs the knowledge and judgment of our acts. St. Thomas Aquinas identifies 8 integral parts of prudence which are necessary for a perfectly prudent act: Memory, Understanding, Docility, Shrewdness, Reasoning, Foresight, Circumspection and Caution.

We may not formally cooperate in evil by doing it, intending it, encouraging it, flattering it, or approving of it. We may sometimes tolerate material cooperation under certain conditions described in the Church’s teaching on moral cooperation and on the Principle of Double Effect.

Citizens have co-responsibility for society. In democracies, the principal political expression of this responsibility is voting. In indifferent elections, those between two worthy candidates, the duty to vote is slight.

However, when a good candidate opposes an unworthy one, voting is more seriously obliged. Worthiness is judged by 1) the issues and 2) the worthiness of the candidates. One may even vote for a political enemy of morality and freedom, but only to exclude a worse one.

In determining which candidate is a greater threat to morality and liberty, we must distinguish between non-negotiable issues and negotiable issues.

Non-negotiable issues, because they involve essential moral goods (e.g. life, liberty), are the most important. Essential goods directly oppose intrinsic evils, which may never morally be chosen.  Thus, the moral tradition speaks of protecting morality as intrinsic to voting.

Negotiable issues, on the other hand, are not matters of essential goodness or evilness. Rather, they involve determining the best means, or policies, to achieve good ends. If the essential good is life, then policies that foster the maintenance of life (e.g. health care, public safety, etc.), must be argued and negotiated.

There are even more specific topic pages than are shown above, which enumerate in greater detail a host of non-negotiable and negotiable issues, so be sure to go to the site to check them out!