A common religion yet Joe Biden and Paul Ryan are separated by abortion issue

The two men almost certainly understand each other on a level no amount of briefing could provide

Joe Biden's prep team for tomorrow's vice presidential debate with his fellow Catholic Paul Ryan has asked him to just this once resist the temptation to explain himself on the abortion issue. There are dangers in that thicket, and he mustn't wander off into a disquisition on the various views of when life begins. (The plan instead? Stock answer, pivot. What could go wrong?)

Plenty, of course. And with the momentum in Romney-Ryan's favor, America's first Catholic vice president is under even more pressure than the man who wants to become the second.

Both not only practice their common faith but have been shaped in important ways by it. "My idea of self, of family, of community, of the wider world comes straight from my faith,'' Biden said in his book "Promises to Keep.'' The vice president, whose mother once counseled him to put off any decision about the priesthood until after he'd gone on some dates, brought the rosary he prays with daily to the Situation Room as the Navy SEALs closed in on Osama bin Laden. He never misses Mass. His trip planners regularly scout for parishes where there'd be no big fuss over him - and no risk of him being denied Communion over his pro-choice politics.

Ryan, a former altar boy, is just as serious in his practice, and on the day his vice presidential nomination was announced he was introduced by Mitt Romney as such: "A faithful Catholic, Paul believes in the worth and dignity of every human life." The congressman and his wife, Janna, send their kids to their parish school in Janesville, Wis., and he has many friends in the clergy, including Cardinal Tim Dolan of New York.

Having grown up in the same culture, the two men almost certainly understand each other on a level no amount of briefing could provide. Yet they also almost perfectly embody the split in the American church, as well as in American politics, with Biden representing the old-school, union-tied, Vatican II generation of Kennedy-loving Catholics whose focus is social justice and who are comfortable with questioning. He was praised for being the only kid in his ninth-grade theology class who copped to doubts about transubstantiation, and his mother famously instructed him, when she heard he was meeting the pope, "Don't you kiss his ring!"

Ryan, meanwhile, upholds the younger, more conservative, John Paul II-era, anti-abortion-focused Catholicism of the sonogram generation. It's doubtful that the different faith-based emphases of these two running mates will influence the election much, despite the efforts of Ryan's cheering section.

But the religious makeup of our country is being dramatically reshaped by politics. According to a Pew study released Tuesday, Democrats are increasingly turned off by conservative politics coming at them from the pulpit, and they are fleeing all religious institutions they perceive as being co-opted by the right. Immigrants have so far allowed the Catholic Church to hold steady despite these defections, but one in five Americans now self-identifies as religiously unaffiliated, even if 68 percent of these folks also say that they believe in God. Their number is expected to keep growing, too, since among Americans under 30, one in three is now unaffiliated.

I certainly don't see the church backing off in an effort to win back those members who are fleeing homilies that make them squirm. But I am sorry that the two halves of Catholic teaching remain as divided as the two men who Thursday will offer their competing visions of what matters.

What Biden could learn from Ryan is that the vice president's insistence that he doesn't want to impose his morality on anybody in a pluralistic country doesn't really track; the Civil Rights Act imposed morality on lots of people, and thank goodness. And same-sex marriage is doing the same, isn't it?

What Ryan could learn from Biden is that, as the National Catholic Reporter's Sean Michael Winters puts it, the leading cause of abortion in this country is poverty, and Ryan's proposal to cut Medicaid would surely increase the number of procedures.

Many Catholic leaders stick with the Republicans because they keep promising to overturn Roe v. Wade, but they don't ever deliver on that promise, and won't. As even strongly pro-choice Nancy Pelosi told me recently, "Let's face it, the Republicans have had the House, Senate and White House any number of times; they could have overturned Roe and they didn't.''

She's right about that. And Catholic leaders such as Bishop Thomas Paprocki of Springfield, Ill., who recently wrote on the subject of abortion and the upcoming election that "a vote for a candidate who promotes actions or behaviors that are intrinsically evil . . . places the eternal salvation of your own soul in serious jeopardy" might want to consider whether 40 more years of supporting Republicans based on that promise would be any different.

Meanwhile, they are not only running off those Catholics who don't agree, but are unwittingly whittling away at their own influence with the increasingly secular Democratic Party. Strong Catholic voices like that of Biden, who argued against the Health and Human Services mandate, will matter less going forward - and there will be fewer Joe Bidens in the party to speak up for them.