Say you’re campaigning for president in Pennsylvania, where Catholics constitute roughly a third of the Democratic electorate, and a Gallup poll shows you badly trailing your rival among Catholic voters. You just lost Catholic voters by nearly two-two-one in Ohio. At that point, the single most important endorsement to be had in the Keystone State would be from Senator Bob Casey Jr., the state’s highest-ranking Catholic. That’s what’s happened this morning to Barack Obama.

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