Correction: The column incorrectly said that U.S. Catholic bishops denied Communion to Sen. Edward M. Kennedy (D-Mass.) after he became a supporter of abortion rights. A Massachusetts bishop wrote a letter faulting the senator’s views in 1975, but Kennedy was not denied Communion.

Near the end of Thursday’s debate, moderator Martha Raddatz asked a question designed to elicit from Vice President Biden and Rep. Paul Ryan dramatic answers about their faith and the most divisive social issue of the 20th century, if not the 21st. “Tell me,” she said, “what role your religion has played in your own personal views about abortion.”

Noting that for the first time in history, the Democratic and Republican vice-presidential nominees are both Roman Catholic (and evoking, therefore, a half-century of conscientious struggle and division among Americans of that faith), she urged the men to answer as personally as possible.

“Please,” she pleaded, “this is such an emotional issue for so many people in this country.”

Unfortunately, each man played it safe, sticking to his party’s script. In 2012, a Democrat running for high-level office can’t get elected if he opposes abortion rights. A Republican can’t get elected if he supports them. Such is the state of the American political arena: Independent thinkers are punished. “Blue Dog” Democrats, moderates who often express reservations about abortion rights, have dwindled from a powerful coalition during the 2009 health-care debate to an impotent group that this newspaper has called “a dying breed.” Republicans who support abortion rights seem even more endangered.

The moral questions raised by abortion may be complex to the point of causing psychic pain for individuals, but the men in line to be president can’t cop to such nuance. Each may have been carrying a rosary in his pocket, but he knew what he needed to say.

Ryan, a Wisconsin Republican, nodded to his spiritual seriousness, saying, “I don’t see how a person can separate their public life from their private life or from their faith,” before veering away from God and insisting that his antiabortion views are based in “reason and science.” He used a well-rehearsed argument in antiabortion circles: The heartbeat on an early sonogram proves that life begins at conception. Having seen images of his eldest child, Liza, a tiny, throbbing bean in utero, he continues to call her “Bean” to this day. Ryan then endeavored to inflame his base by raising the specter of a government-sponsored health-care plan that tramples religious liberties by insisting that Catholic institutions provide contraception despite their religious principles.

Biden also appeared sincere when he said, “My religion defines who I am.” He acknowledged that he parts ways with his church’s doctrine on abortion, saying that, personally, he would submit to religious authority but that as a lawmaker, he would not impose his religious beliefs on others. He emphasized the “open-mindedness” of his party by talking about the Supreme Court justices President Obama has chosen. Biden, too, tried to excite his base, in his case by raising questions of social justice — and care for the poor — in the context of his faith, but neither Raddatz nor Ryan seized the bait.

Raddatz must have hoped for something more when she asked that question. I would have. She must have hoped that as fathers and husbands, Biden and Ryan might have been able to imagine out loud how they would feel if confronted in real life with the possibility of abortion. Might they have acknowledged that a hard religious or political line is easy to hold in principle but far more difficult in practice?

She must have hoped for a broad acknowledgment of the agonies American Catholics have suffered at the hands of this question, leaving a majority of them, 50 years after Vatican II, at odds with their bishops. She must have been thinking about the recent Gallup poll showing that more than half of Americans want abortion to be legal in certain cases and more than half of them think it’s morally wrong. How much overlap is there between those two groups? A lot, I suspect.

Perhaps Raddatz was thinking of that most eminent Catholic politician, the late senator Edward Kennedy, who — having grown up before Roe v. Wade — struggled mightily with the religious and political implications of the abortion question.

Before he became the man the bishops liked to make an example of, Kennedy took a position consistent with this church. “When history looks back to this era,” he wrote to a constituent in 1971, “it should recognize this generation as one which cared about human beings enough to fulfill its responsibility to its children from the very moment of conception.”

Kennedy later came out as an abortion-rights supporter because his party and his ambitions required it of him, but in private his personal and religious beliefs were far more complex. In the end, he understood that religious talk in public is almost always a political manipulation. Thursday’s debate proved him right.

To read Lisa Miller’s previous columns, go to onfaith.