The recent publication of "Daniel Patrick Moynihan: A Portrait in Letters of an American Visionary" (Public Affairs) is cause for both celebration and sadness: celebration, because his letters reintroduce us to Pat Moynihan's scintillating intellect, sparkling wit, and penetrating insight into some the great issues of the late 20th century; sadness, because Pat was, in his time, the great Catholic "what if...?" of American public life.

Following the biblical injunction in Sirach 44:1, let us [first] praise famous men.

Daniel Patrick Moynihan was one of the five or 10 most influential public intellectuals of the past half-century, a man whose ideas eventually worked themselves into the hard soil of public policy. He was among the first to recognize the enduring influence of ethnicity in the political and cultural Mixmaster of modern America, as he identified early on the social pathologies destroying the African-American family -- and he was pilloried as a racist for both insights. When most of the Democratic Party went into a post-McGovern swoon of appeasement and neo-isolationism, Pat helped lead the charge for a robust U.S. foreign policy focused on the defeat of communism through the defense of human rights. Long before welfare reform came onto the national radar screen, Moynihan knew that something was desperately wrong with our social services and coined the pellucid phrase "defining deviancy down" to describe the wishful thinking and counter-productive welfare policies then destroying lives, families and neighborhoods.

And along the way, he became the only man in our history to serve in the cabinet or sub-cabinet of four consecutive presidents of two different parties: Kennedy, Johnson, Nixon and Ford.

That public service, which culminated in his 1976 election to the first of four terms in the United States Senate, was marked by a rapier-like wit and a bracing, combative public presence. As U.S. ambassador to the United Nations, he raised polemics to a new art form while flagellating various corrupters of the moral coin of international public life; his speech condemning the General Assembly's infamous "Zionism is racism" resolution remains a landmark in the annals of passionate advocacy. As for the wit, well, asked once whether it was true that he had been sick throughout his years as ambassador to India, Pat replied, "I was only sick once! It lasted two and a half years!"

For all of these reasons, it seemed to some of us, in the late 1970s, that Pat Moynihan was singularly positioned to do several things at once: save the Democratic Party from its nose-dive into the fever swamps of the Sixties; bring a new bipartisan realism to social welfare policy; remind us that a healthy culture was important for democracy; give America back a sense of itself as a protagonist of the history of freedom. In doing this, he might have uniquely embodied, in our high politics, the insights of Catholic social doctrine and the Catholic optic on world affairs.

Alas, it was not to be. For whatever reasons -- New York state politics and fear of the then-influential New York Times likely high among them -- Pat did virtually nothing about the great civil rights issue of the late 20th century: the defense of the right to life. He famously said that, while everyone is entitled to their own opinion, no one is entitled to their own facts. And no one as intelligent as Daniel Patrick Moynihan could have been ignorant of the scientific facts about the product of human conception, the moral facts about the ethical status of the pre-born child, and the jurisprudential facts about the travesty of legal reasoning that produced Roe v. Wade. Yet, until an end-of-career vote against partial-birth abortion, Pat Moynihan was not a happy warrior for life, as he had been a happy warrior for other great causes.

This was more than a sadness, a failure of insight and nerve. It marked, I believe, the greatest lost opportunity to bring the full range of Catholic insights to bear in public life in my lifetime.

George Weigel is Distinguished Senior Fellow of the Ethics and Public Policy Center in Washington, D.C.