For some people, it's such a sensitive topic they would prefer no one discussed it at all. But if Samuel Alito is confirmed to the Supreme Court, it will be the first time in American history that five sitting justices will be Catholic: Alito, John Roberts, Clarence Thomas, Antonin Scalia and Anthony Kennedy.
Approximately 25 percent of the U.S. population is estimated to be Catholic, so a minority religion would be the majority on the court.
It tends not to be something people make an issue out of, at least publicly, but some liberals do have concerns about such a Catholic court.
"There is some fear that they might perhaps, on some issues like abortion, carry out a kind of Catholic jurisprudence rather than reflecting a broader point of view," said John Green, a senior fellow at the Pew Forum on Religion and Public Life.
But for others, Alito's confirmation represents a milestone for a once-oppressed religious minority.
It wasn't so long ago, as Sen. Pat Leahy, ranking Democrat on the Senate Judiciary Committee, brought up during the Alito hearings: "The signs then were 'no Irish need apply' or 'no Catholics need apply.'"
A good deal of anti-Catholicism, Green says, was a staple of American politics.
"Some of this had to do with how the United States was settled," he said. "Some of the original settlers were Protestants who fled Europe because of the then-problems with the Catholic Church. And among many of those Protestants, there was this fear that the Roman Catholic Church through the Vatican would dictate the behavior of American politicians -- so that senators and governors and perhaps even a Catholic president, would answer to the pope and be a Catholic first rather than an American first."
In 1928, Al Smith -- the first major-party Catholic presidential candidate -- was the subject of withering anti-Catholic propaganda.
He even saw a fellow Democrat denounce his candidacy on the Senate floor, warning Americans that Smith's candidacy would mean the Roman Catholic Church "will lay the heavy hand of a Catholic state upon you and crush the life out of Protestantism in America."
In 1960, John F. Kennedy traveled to Texas to defend himself to a group of Houston ministers. That was after his candidacy was condemned by the Southern Baptist Convention, which unanimously passed a resolution voicing doubts that any Catholic should be president.
"I am not the Catholic candidate for president," Kennedy said. "I am the Democratic Party's candidate for president, who happens also to be Catholic. I do not speak for my church on public matters -- and the church does not speak for me."
"I remember that campaign," said Richard Land, president of the Southern Baptist Convention's Ethics & Religious Liberty Commission. "I was 14 years old, and I lived in Houston, Texas, and my pastor came back to our Baptist church and from the pulpit, he said: 'I have good news! President Kennedy told us that on public-policy issues, his church doesn't speak for him and he doesn't speak for his church. And that he's going to separate his Catholicism from his service if he's elected.' And people applauded all across the auditorium. They just thought it was a great thing."
That was 45 years ago. Today's silence on the issue is notable even to some Catholics.