I am of a generation that learned from Sister in eighth grade that we should cultivate ideals rather than ideology; that we should strive to be reasonable rather than unreasonable, “ideology” being defined by Sister as the latter, while “ideals” were principles that stood the test of right reason.
We rightly expect our laws to be based on ideals, not ideology. Ideals denote a process of deliberation, a search for truth that involves a willingness to recognize error and to self-correct. Ideals presuppose transcendent truth and our ability to discern it.
Ideology requires none of that; it merely requires a pledge of allegiance to a preferred idea with no need for correction. In fact, correction is unthinkable because ideology, while often scorning objective truth, relies on the concept for its own justification.
The Founding Fathers realized that ideology, thus defined, could give rise to a mob mentality. Yet despite the danger, they embarked on this grand experiment of government by the people. They did so because they believed that, in the end, ideals would trump ideology in the human heart; that the force of right reason was strong enough to make certain truths self-evident.
Of course these ideals rested on their belief in God and His Word. Several generations now have largely failed to pass on even the basics of the religious heritage they received. So the question becomes: can this system, based on the recognition that God exists, long endure?
Catholics understand that the formation of the conscience and the cultivation of virtue that make self-government possible is a lifelong task. To develop a right conscience, we draw on many sources, including the word of God, the teachings of the Church, and the advice of others. To develop the virtues, we rely on the grace flowing from the sacraments and prayer. These are gifts of inestimable value and effectiveness.
But what of the growing number who claim no church membership or who do not believe in God? Can their consciences serve them adequately as citizens? Can they develop the virtues needed for self-government? Or are they a sign that the experiment is entering its end game?
In his first encyclical, Lumen Fidei, Pope Francis (building on a text partly finished by Benedict XVI) points out that “Anyone who sets off on the path of doing good to others is already drawing near to God, is already sustained by his help, for it is characteristic of the divine light to brighten our eyes whenever we walk towards the fullness of love.” 
This is an important reminder and should give us hope. The person of good will, even if a non-believer is already experiencing the help of God. His conscience is being enlightened day by day. As long as he continues down that road, he can make progress in right reason, forming ideals rather than becoming a slave to ideology. The necessary ingredient is good will. While it is not as reliable as Church teaching, it ensures that the heart remains open to what Cardinal Newman called the “aboriginal Vicar of Christ” – conscience.
I’ve often felt that one observation (at times attributed to P.T. Barnum, at times attributed to President Lincoln, at times attributed to an unidentified journalist) gives a better defense of the possibility of our form of government than most others: “You can fool some of the people all of the time, and all of the people some of the time, but you cannot fool all of the people all of the time.”
As Americans, we rely on that last point – that you cannot fool all of the people all of the time. Although it seems a weak and messy foundation, it does not contradict Church teaching on the distinction between the political community and the Church.
In 2007, the Congregation for the Doctrine of the Faith issued a doctrinal note  on this subject. It is worth reading in its entirety; almost every line is quotable. But this one seems particularly important: “Christian faith has never presumed to impose a rigid framework on social and political questions, conscious that the historical dimension requires men and women to live in imperfect situations, which are also susceptible to rapid change.”
Imperfect situations; these we will always have with us. The “Note” goes on: “The Church. . .is at once a sign and a safeguard of the transcendent character of the human person.”
History shows that it is actually more difficult to sustain ideology than ideals over the long run. And this makes perfect sense. In the end, it is the transcendent character of the human person supported by God’s grace that makes our form of government possible.