“The two candidates are running two different kinds of races,” said John Dickerson, the moderator of “Face the Nation” on CBS, who has interviewed both Mrs. Clinton and Mr. Trump on his show.

“At every opportunity possible, you invite both of them on to share their views and answer the questions of the moment,” Mr. Dickerson said. “But a lot of this is on the candidates. If they believe a point is better expressed by their surrogate, or not talking at all, that’s sort of their choice.”

Networks are seeking novel ways to maintain balance, like staging voter town halls that provide candidates with equal airtime; seeking a wider spectrum of on-air contributors and campaign surrogates; and bringing more fact-checking into segments, as Jake Tapper has done recently on CNN to some acclaim.

Still, the presence of Mr. Trump can be irresistible, especially in an election in which viewership and advertising rates have soared, generating tens of millions of dollars in additional revenue for an industry threatened by digital competition.

Last week, none of the three major cable news networks — CNN, Fox News, or MSNBC — carried Mrs. Clinton’s speech to a workers’ union in Las Vegas, where she debuted sharp new attack lines against Mr. Trump.