How far Mr. Trump goes with that convention approach, first reported by Jeremy W. Peters of The New York Times last week, remains to be seen; one never knows. But some of it promises to border on spectacle, to put it mildly. (Let me repeat: Among the potential themes is Mr. Clinton’s sex life.)

It could be one of those events that we look back on as a defining moment in American media, especially for the television networks: Did they once again this year hand themselves over to a Trumpian infomercial — the ultimate Trump infomercial — and bask in the ratings?

Or did they rediscover their vital role of providing context, perspective and truth in a contest that is not a countdown-clock-worthy sporting event or reality show, but a competition for the presidency of the United States in fraught and dangerous times?

Truth will not come to the fore without hard work and, potentially, a fight.

The robust fact-checking industry that has sprung up over the past several years will have to work overtime during both conventions. But while Mrs. Clinton’s dossier of falsehoods has increased with the F.B.I. report contradicting so many of her statements about her private email server, Mr. Trump and his campaign have generated so many untruths that Factcheck.org declared that in the 12 years since its founding, “we’ve never seen his match.” And that was before this year began.

His convention could surprise everyone and stick to only verified attacks, while coming off as a more traditional affair. But many of Mr. Trump’s expected convention subjects have generated their share of false, unsubstantiated or wildly exaggerated assertions — that Mrs. Clinton “slept through” the Benghazi attack (false); that the current administration is financing illegal immigration (false); and that it is not vetting refugees from the Middle East (false).