It's been a week marked by mistakes, some new and some continuing.

The pro-Obama Super PAC ad that essentially blames Mitt Romney for a woman's death from cancer is over the line, and if it's allowed to stand the personal attacks that have marked the presidential campaign will probably get worse. If the president rebukes the PAC and renounces the ad—and he should, and he'd look better doing it than not doing it—then we'll all know there's an ethical floor below which things can't sink. The ad was a mistake for a number of...