Two years ago, Democrats and supporters of presidential candidate Barack Obama were hoping for “change.” Now it’s the Republicans’ turn.

They hope people will give the GOP the upper hand in the midterm elections Nov. 2, granting them control of Congress.

That very well may happen — at least in the House of Representatives.

Change is the nature of politics.

But there are things that don’t change in the ebb and flow of power. And as the nation considers the direction it wants to take, two years after it elected Obama and gave his party a majority in Congress, it’s a good time to recall the principles that should guide our decision-making in the voting booth.

For many years, the U. S. Conference of Catholic Bishops has tried to help us do that, publishing a guide to politics every four years. Two years ago, the bishops released “Forming Consciences for Faithful Citizenship: A Call to Political Responsibility From the Catholic Bishops of the United States.”

There’s no question that Catholics have a right to participate in politics. In fact, we must, say the bishops. “The Church’s obligation to participate in shaping the moral character of society is a requirement of our faith,” states “Forming Consciences for Faithful Citizenship.” “We encourage Catholics throughout the United States to be active in the political process, particularly in these challenging times.”

Bishops and priests are Catholic citizens as well, and no matter how many people yell and scream that they have no right to interfere, they too should feel free to speak out on crucial matters of the day in the public square. The laity, indeed, need their wisdom and guidance.

It is not a matter of voting Republican or Democratic. It is a matter of supporting candidates and policies that are good for human welfare and society’s peace and tranquility. In other words: the common good.

The Church’s obligation to participate in politics, “Forming Consciences” explains, “is a basic part of the mission we have received from Jesus Christ, who offers a vision of life revealed to us in sacred Scripture and Tradition. To echo the teaching of the Second Vatican Council: Christ, the Word made flesh, in showing us the Father’s love, also shows us what it truly means to be human (see Gaudium et Spes, 22). Christ’s love for us lets us see our human dignity in full clarity and compels us to love our neighbors as he has loved us. Christ, the Teacher, shows us what is true and good, that is, what is in accord with our human nature as free, intelligent beings created in God’s image and likeness and endowed by the Creator with dignity and rights.”

“To love our neighbors as he has loved us.” That’s pretty much what it all boils down to. That is the basic principle that should be behind every choice and behind every issue — be it abortion, immigration, the economy or the war on terrorism.

As the document continues to explain: “What faith teaches about the dignity of the human person and about the sacredness of every human life helps us see more clearly the same truths that also come to us through the gift of human reason. At the center of these truths is respect for the dignity of every person. This is the core of Catholic moral and social teaching. Because we are people of both faith and reason, it is appropriate and necessary for us to bring this essential truth about human life and dignity to the public square.”

“Forming Consciences” continues: “We are also called to promote the well-being of all, to share our blessings with those most in need, to defend marriage and to protect the lives and dignity of all, especially the weak, the vulnerable, the voiceless.”

The most vulnerable and voiceless among us are still the unborn — a group of Americans who enjoy even less legal protection than black slaves did in an earlier age. In spite of Obama’s pledge to seek “common ground” on the issue of abortion (notably at his May 2009 speech at the University of Notre Dame) and in spite of his recent echoing of former President Bill Clinton’s formulaic hope of seeing abortion “safe, legal and rare,” the past two years have seen too many setbacks for the unborn. Just one example: Americans are now being forced to pay, through their tax dollars, for the deliberate killing of human embryos — their little brothers and sisters in the first days of their existence — so that their most prized possession (stem cells) may be extracted and put to work in research that may one day yield a cure for people suffering from Alzheimer’s, Parkinson’s, cancer and a host of other ailments.

We don’t use this as an example to urge readers to vote Republican either. After a federal court imposed a temporary injunction on federal funding of human embryonic stem-cell research, some members of Congress and others called for the permanent retirement of the Dickey-Wicker Amendment, a renewable appropriations-bill rider that forbids using federal funds for research “in which human embryos are created, destroyed, discarded or knowingly … subjected to risk of injury or death.” Candidates came out on the issue as well. In Connecticut, the Democratic candidate for the U. S. Senate — state Attorney General Richard Blumenthal — vociferously added his support for such a move.

Not to be outdone, so did the Republican candidate, Linda McMahon, the wife of pro wrestling entrepreneur Vince McMahon.

A small lesson in the danger of assuming that all Republicans are conservative and pro-life, no matter how they characterize their Democratic rivals.

For Catholics who find their own local races to be similarly confusing, it’s well to bear in mind what the bishops have advised in “Forming Consciences:” “The Church calls for a different kind of political engagement, one shaped by the moral convictions of well-formed consciences and focused on the dignity of every human being, the pursuit of the common good, and the protection of the weak and the vulnerable.”

It’s worth a reread.