Stephen Schenck, a political scientist at The Catholic University of America and an Obama supporter, said that while parishioners don't base their vote on what bishops say about a particular lawmaker, church leaders give "a kind of moral legitimacy to participation in politics, a kind of permission slip to feel good about your candidate."
Both Biden and Ryan have had their share of quarrels with bishops.
Biden personally opposes abortion and has voted against public funding for the procedure, but supports abortion rights. As a result, a Delaware bishop in 2006 threw out plans to name a Catholic school building for the lawmaker and other bishops have called Biden's — and Obama's — support for legalized abortion immoral.
Ryan also opposes abortion, but has sparred with bishops over cuts to social programs in the 2013 House Republican budget plan.
The congressman drafted then defended the proposal by citing Catholic moral theology. The congressman said his budget plan was grounded in church teaching on helping the poor, which he explained could be accomplished if Americans "don't make people dependent on government."
He cited the Catholic concept of "subsidiarity," or finding solutions at the lowest level possible in society, such as families and local government.
Leaders of the bishops' social justice and peace committees complained to House leaders that, "a just spending bill cannot rely on disproportionate cuts in essential services to poor and vulnerable persons." The bishops voted 171-26 at a national meeting in June to draft a lengthier statement explaining why. The statement won't be released until after the election.