When Jim Lehrer takes the stage in Denver on Wednesday night, the tens of millions of people watching will see the same imperturbable voice of reason they have come to know in his quarter century as the country’s go-to referee for the presidential debates.

But Mr. Lehrer, the former anchor of “PBS NewsHour,” has been seething. He said he was outraged by suggestions that he was a “safe” and uninspired choice to moderate the first of four debates. And he is offended by reports that questioned whether this — his 12th presidential debate — might be one too many.

“It’s a rough, rough world — I know that,” Mr. Lehrer said recently, his voice rising in exasperation. “And those of us who have decided to play in that world have to play by those rules. I’m susceptible to the same smears as anyone else.”

In this election, living by the journalist’s doctrine of disengagement — the reporter is never the story — has proved harder than ever, especially for those moderating the debates.