Why Chris Wallace likely won’t be fact-checking during Tuesday’s presidential debate

The big media event of the week — well, as far as we know as of now — is Tuesday night’s presidential debate. Fox News’ Chris Wallace will moderate the first of three scheduled presidential debates. (There also will be one vice presidential debate.)

So what is the role of a moderator? To ask good questions on a variety of topics and to keep the candidates focused on those topics. A good moderator also needs to make sure the candidates answer the questions asked if they try to pivot or...