But it was a large, insensitive error. The Vatican admitted that Williamson's Holocaust denial was "unknown to the Holy Father at the time he revoked the excommunication." Not only the Obama administration struggles with an incompetent vetting process.

The stakes of such failure, however, are higher for the Vatican. Christianity -- still accused by the anger of genocide survivors and haunted by the unquiet ghosts of Auschwitz and Kigali -- cannot tolerate leaders who deny the Holocaust without adding to its greatest scandal and further discrediting its deepest ideals.

Benedict has ended up at the right place, demanding that Williamson recant his statements. But serious damage has been done because the wounds are so recent, and the historical offense so massive.

While Christian resistance to the Holocaust was rare, there were exceptions. Bernhard Lichtenberg, the provost of St. Hedwig's Cathedral in Berlin, was convicted of violating the Sedition Law after two parishioners informed on him to the Nazis. The judge summed up his crime as follows: "On 29 August 1941, the defendant held evensong ... before a large congregation. He closed the service with a prayer in which he said, among other things: 'Let us now pray for the Jews and for the wretched prisoners in the concentration camps.' ... He states that he has included the Jews in his prayers ever since the synagogues were first set on fire and Jewish businesses closed."

Lichtenberg served two years in prison and died on the way to Dachau. A church dedicated to his ideals cannot be the church of Bishop Williamson.