Who owns the 'Catholic vote'? Roughly 40 percent of Catholics are reliable Republicans, and 40 percent are reliable Democrats. The rest could go either way. That makes Catholics the ultimate swing voters.

AT A MEETING OF CATHOLIC PUNDITS IN NEW YORK, National Review columnist Kate O'Beirne told the story of two old friends, Pat and Mike. When Pat told Mike that he heard that Sean O'Connor, a friend of theirs, had voted Republican, Mike responded with outrage. "That's a dirty lie!" he said. "I saw him at Mass."

The political allegiance of Catholics today is a question much disputed, but it wasn't always so. For decades the alliance of Catholics with the Democratic Party was a given--so much so that the partnership became the subject of innumerable jokes, some of which are still trotted out from time to time.

Jokes like O'Beirne's, from the rich reservoir of the Irish-Catholic Pat-and-Mike series, are a sharp reminder of how much things have changed. Back in the days of Pat and Mike, Catholics had a comfortable home in a political party. Today, it is often said that Catholics are politically homeless--driven away from the Democratic Party by the polarizing issue of abortion, yet uncomfortable with Republican stances on the free market and the death penalty. Because of their divided loyalties, Catholics are now the ultimate swing voters: Since 1972, the presidential candidate who won the Catholic vote also won the election. (The one exception was Al Gore in 2000, and he won the popular vote.)

George W. Bush has made significant inroads among Catholic voters because he has used language--and chosen issues--that appeal to Catholics. "Compassionate conservative," after all, is a term that could describe many Catholics, who are conservative on social issues yet favor government programs for the poor. With the 2006 election in sight, the big question is whether Republicans can win the Catholic vote again or whether the Democratic Party can woo them back to the party of their forebears. There are signs that the Dems may be able to do so, especially since they seem willing to enlarge the party's tent to include pro-lifers such as Bob Casey Jr., a Senate candidate in Pennsylvania. If the Democrats are successful, they would renew an alliance that has deep roots in American history.

CATHOLICS WERE NOT a notable presence on the U.S. political scene until the 1830s and 1840s, when the Germans and Irish began arriving in large numbers. These immigrants faced strong opposition from the Know-Nothings and other nativist groups who feared that the immigrant hordes represented a papist invasion. Catholics opted to join the Democratic Party because it was friendlier to minority groups than the Protestant-dominated Whigs and the Republicans, who were seen as too accommodating to nativists.

The partnership between Catholics and Democrats was not always amiable. At the turn of the century, divisions erupted in the party between Catholics and party leaders in the South and West. Among the forces that drove them apart was the candidacy of William Jennings Bryan in 1896. Bryan supported Prohibition and opposed parochial schools, which did not sit well with Irish Catholics. Irish Americans were also upset when, 20 years later, Democrat Woodrow Wilson decided to enter the Great War on the side of the hated British.

Over time, Catholics established a firm grip on local Democratic political machines. In cities such as Boston, New York, and Chicago, Catholics were a political force to be reckoned with, and before long they were wielding their power on the national scene. In 1928, the Democrats nominated Catholic Alfred E. Smith of New York for the presidency, a sign of Catholic influence within the party. Yet the formidable political power of Catholic Democrats in urban centers was not enough to prevail in a national election, and Hoover won in a landslide.

While Catholics may have lost the White House, they remained a potent intellectual and political force within the Democratic Party. Local Catholic party chieftains helped get out the vote, while Catholic thinkers such as Monsignor John A. Ryan provided intellectual support for the New Deal. Ryan was dubbed the Right Reverend New Dealer for his advocacy on behalf of Franklin Delano Roosevelt and the progressive economic reforms of the New Deal, which he believed were in line with Catholic social teaching.

Catholic support for the Democrats continued strong throughout World War II and afterward. Many Catholics switched parties in 1952 to support the moderate Republican Dwight Eisenhower, and a majority voted for his re-election in 1956. But Catholics returned in force to support Kennedy, who would be the first Catholic to win the presidency. Close to 80 percent of Catholics cast their votes for Kennedy, an unprecedented show of support that would not be repeated.

FISSURES IN THE Catholic-Democratic alliance began to develop in the late 1960s. The standard account of the Catholic exodus from the Democratic tent maintains that the party's support of Roe vs. Wade was the motivating factor. Yet Notre Dame sociologist David Leege argues that the issue of race was perhaps more crucial. Beginning in 1968, Republicans actively courted white ethnic voters (read Catholics) who felt besieged by the growing number of minorities moving into cities. Catholic middle-class workers had to compete with these newcomers for jobs, and they resented the fact that minorities received government benefits.

The election of 1972 proved to be crucial in the Catholic-Democratic partnership. Dissatisfied by the liberal social views of George McGovern, a majority of Catholics voted for Nixon. That year also saw a change in Democratic strategic alliances that would have long-term effects on the influence of Catholics within the party.

The primary architect of the new strategy was Fred Dutton, who argued in a 1971 book, Changing Sources of Power: American Politics in the 1970s, that the Democrats should break with Catholics since they "have tended ... to become a major redoubt of traditional Americanism and of the anti-negro, anti-youth vote." As a member of the McGovern commission of the Democratic Party, Dutton helped change party rules to give a greater voice to women and young people and effectively undercut the influence of old (mostly Catholic) party bosses.

The fallout from these changes was evident eight years later, when Ronald Reagan handily won the Catholic vote. During both terms of the Reagan presidency, there was much hand-wringing about the "Reagan Catholics" and why they had been won over by the Republican Party.

Perhaps the most detailed exploration of this historical shift can be found in Samuel G. Freedman's The Inheritance, which follows three Catholic families as they move from Roosevelt Democrats to Reagan Republicans. Freedman describes the political change of a man named Tim Carey. Carey's grandmother was a Democratic organizer during the Depression, yet Carey campaigned for Reagan and later worked for Republican Gov. George Pataki in New York. His political turnabout was precipitated by a 1967 incident. Carey was a soldier at the Pentagon, facing off against anti-war demonstrators, when he heard civil rights activist Dick Gregory say that only "poor blacks" and "dumb whites" were soldiers. That experience alienated him from anti-war groups and drove him toward the Republican Party.

Catholic voters, however, are not a predictable bunch, and in 1992 Bill Clinton received a plurality of the Catholic vote. Clinton used language that appealed to Catholics who wanted to vote Democrat but had qualms about what they perceived to be the party's lax attitude on moral issues. Clinton's pledge to make abortion "safe, legal, and rare" won the support of many Catholics, who felt that was a good compromise in a country where a complete prohibition was unlikely. Clinton's endorsement of traditionally conservative issues--such as school uniforms for children in public school and the "V-chip'--also appealed to many Catholics.

George W. Bush's success among Catholic voters has been well-documented. He hired a special adviser on Catholic issues, and his endorsement of faith-based initiatives and school vouchers won him points among the Catholic electorate. Bush won 47 percent of the Catholic vote in 2000, and then 52 percent in 2004. Conservative pundits have pointed out that he did even better among Catholics who attend Mass at least once a week.

IN THE WAKE of their defeat, the Democrats have tried to lure Catholics back into the fold. The 2006 Pennsylvania Senate race is particularly interesting, since Democrat Bob Casey Jr., a Catholic, is running against perhaps the most prominent Catholic conservative in Congress: Republican Rick Santorum. Casey is the son of the late Pennsylvania Gov. Bob Casey, who was prevented from speaking at the 1992 Democratic convention because of his pro-life views--an incident that still angers many pro-life Catholics. Some people see the Democrats' support for Casey Jr. as an acknowledgment that the party was unfair to his father. The Dems have also given special attention to Virginia Gov. Tim Kaine, a Catholic Democrat, who was asked to respond to this year's State of the Union address.

Meanwhile, Catholic Democratic legislators are out to prove that they, too, are good Catholics. In March, a group of 55 Democratic members of the House of Representatives signed a "Statement of Principles" claiming that "the church as a community is called to be in the vanguard of creating a more just America and world. And as such, we have a claim on the church's bearing as it does on ours." The statement is obviously a response to certain Catholic bishops who, in the 2004 election, strongly implied that it was impossible to be a good Catholic and also be pro-choice. The statement acknowledges the "undesirability of abortion," but overall it does not adequately address the difficulty of the problem facing pro-choice Catholic legislators.

"I ... don't think it was a particularly winning statement," said Margaret O'Brien Steinfels, co-director of the Fordham University Center on Religion and Culture and former editor of Commonweal. "Too much tooing and froing on social justice and too little grappling with abortion."

Richard McBrien, a theology professor at the University of Notre Dame, said he thinks that the formulation of the statement will have a "positive effect" on the legislators "because it gets them thinking at a deeper level about the relationship between their political responsibilities and their Catholic faith."

McBrien predicts that abortion will not be as pivotal in the coming election as it was in the past. "The war in Iraq is the overriding issue, along with traditional economic issues," he wrote. "These are working in favor of Democratic candidates now, as all the national polls are showing."

Perhaps pro-life Catholics are less concerned with the abortion question now that the balance of the Supreme Court is tilting in their favor. Both Chief Justice John Roberts and Justice Samuel A. Alito Jr. are Catholic, and they are expected to turn the court in a more conservative direction on the abortion issue. In addition, midterm elections generally don't energize pro-life voters like presidential contests, when the power to nominate Supreme Court justices is in play.

If abortion is not Topic A for Catholics, what will be the defining issue during the 2006 election? Possibly immigration. Several American prelates have come out strongly against a proposed law that would make it a crime for anyone, including social workers, to provide assistance to illegal immigrants. Cardinal Roger Mahony of Los Angeles has said that if the law passes he will tell his priests to defy it. "Part of the mission of the Roman Catholic Church is to help people in need," Mahony wrote in an op-ed in The New York Times. "It is our Gospel mandate, in which Christ instructs us to clothe the naked, feed the poor, and welcome the stranger."

The church's stand on immigration has provoked anger among some Republican legislators, who have suggested that the church should lose its tax-exempt status. This issue could drive a wedge between Catholics and Republicans, hurting the GOP in 2006. McBrien said that the immigration debate proves that "Catholics on both sides of the spectrum practice what some call 'cafeteria Catholicism.'"

"Democrats have been severely criticized for their ignoring church teaching on sexual issues, but Republicans also pick and choose from the Catholic agenda," he said.

The immigration debate proves, once again, that Catholics are a restless people, never completely at home in any political party. Writing in the 1830s, Alexis de Tocqueville wondered, in sociologist David Leege's words, "if Catholic communitarian and egalitarian values would fit well into a democracy based on freedom and individualism." The question is still on the table.

Maurice Timothy Reidy is an associate editor at Commonweal magazine.