Paul Ryan knows that Catholic social doctrine is not some sort of doughnut machine that plops out ready-made answers to complex questions of public policy. There is no — repeat, no — direct line from the principles of Catholic social doctrine to judgments on levels of WIC funding, food-stamp funding, or Pell Grant funding, three issues on which the Georgetown faculty claims moral certainty when the relevant mode of moral analysis is prudential judgment. Ryan knows that and is prepared to explain why that’s the case. That willingness, plus Ryan’s refusal to concede the moral high ground to the Catholic Left in the public-policy debate, plus the intelligence, good humor, and conviction he brings to these arguments, helps explain why he’s the Catholic Left’s worst nightmare. The Catholic Left recognizes that; and thus, predictably, things have turned chippy, even ugly.