Jean Bethke Elshtain is kind of a big deal in political philosophy. She is not, however, a moral theologian, nor is she Catholic, so she makes an odd source for Marc Thiessen to quote (introducing her as "one of America's great moral theologians") in explaining the Catholic moral concept of casuistry.
Still, the author gets to choose his own sources, and if his editor okays it he's good to go.
Now, though, I read this in a New York Times's article about the Thiessen affair:
Jean Bethke Elshtain, of the University of Chicago, said that while soldiers or politicians might have to commit necessary evils sometimes, they "still stand convicted before God, if you are thinking theologically."
"The necessary evil means precisely that: it is both 'necessary' and 'evil,'" she said. "So the worst thing that can happen is to make something like waterboarding legally acceptable."
Assuming the reporter didn't mangle it (and from that last sentence, mangling what comes before is a distinct possibility), Professor Elshtain thinks something can be both necessary and evil.
So we have a political speechwriter who doesn't know what "wrong" means turning to a political philosopher who doesn't know what "evil" means for moral instruction.