How big a role did the Church play in this weekend’s House vote on health care reform?

Consider this:

Injecting itself aggressively into the health-care debate, the Roman Catholic Church in America has emerged as a major political force with the potential to upend a key piece of President Barack Obama’s agenda.

Behind-the-scenes lobbying, coupled with a grassroots mobilization of Catholic churches across the country, led the House Saturday to pass an amendment to its health-care bill barring anyone who receives a new tax credit from enrolling in a plan that covers abortion, a once-unthinkable event in Democrat-dominated Washington.

The restriction would still have to be accepted by the Senate, where it will likely face a tough fight. The issue could sink the larger health legislation if the chambers fail to reach agreement, or if any consensus language leads supporters to defect.

The House vote, and the central role played by one of the country’s biggest religious denominations, stunned abortion-rights groups that had worked hard to elect Mr. Obama and expand Democratic congressional majorities. Activists on the left had thought social issues would take a back seat to economic concerns.

The bishops’ success served as a reminder that Democrats’ strategy over the past two election cycles of recruiting more conservative candidates to run in competitive House and Senate seats can have unwelcome policy consequences for liberals among the party’s base. About 40 House Democrats are opposed to abortion rights.

The bishops have a history of political activism. In the 2004 presidential race, some bishops said they would refuse to grant communion to Democratic nominee John Kerry, a Catholic who favored abortion rights. In 2005, the bishops’ conference backed efforts by then-President George W. Bush and Republican lawmakers to intervene in the Terri Schiavo right-to-die case. But rarely has the church entered the fray with such decisive force.

“The Catholic bishops came in at the last minute and drew a line in the sand,” said Laurie Rubiner, vice president for public policy at the abortion-rights advocacy group Planned Parenthood. “It’s very hard to compete with that.”

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