One obvious question going into Wednesday’s forum was whether Mr. Trump would repeat his frequent claim that he opposed the Iraq war from the start. This claim is demonstrably false: His only documented prewar remarks on the subject support the war, and the interview he likes to cite as evidence of his prescience took place more than a year after the war began. But he keeps saying it anyway; if he did it again, how would Matt Lauer, the moderator, respond?

Well, he did do it again — and Mr. Lauer, who used about a third of his time with Mrs. Clinton talking about emails, let it stand and moved on to the next question.

Why is it apparently so hard to hold Mr. Trump accountable for blatant, in-your-face lies? Part of the answer may be that journalists are overwhelmed by the sheer volume of outrageous material. After all, which Trump line should be the headliner for a news analysis of Wednesday’s event? His Iraq lie? His praise for Vladimir Putin, who “has an 82 percent approval rating”? His denigration of the American military, whose commanders, he says, have been “reduced to rubble”?

There’s also a deep diffidence about pointing out uncomfortable truths. Back in 2000, when I was first writing this column, I was discouraged from using the word “lie” about George W. Bush’s dishonest policy claims. As I recall, I was told that it was inappropriate to be that blunt about the candidate of one of our two major political parties. And something similar may be going on even now, with few people in the media willing to accept the reality that the G.O.P. has nominated someone whose lies are so blatant and frequent that they amount to sociopathy.

Even that observation, however, doesn’t explain the asymmetry, because some of the same media organizations that apparently find it impossible to point out Mr. Trump’s raw, consequential lies have no problem harassing Mrs. Clinton endlessly over minor misstatements and exaggerations, or sometimes over actions that were perfectly innocent. Is it sexism? I really don’t know, but it’s shocking to watch.

And meanwhile, if the question is whether Mr. Trump can really get away with his big liar routine, the evidence from Wednesday night suggests a disheartening answer: Unless something changes, yes he can.