I’ve been bingeing on a lot of anti-Hillary Clinton books lately. Some of their gripes are legitimate and verifiable; some are halfway down the six-lane expressway to bonkersville. But of all the unlikely themes to emerge from them, of all the conspiracies they propose and the outrages they cite, the strangest of all is quite straightforward: that Mrs. Clinton is a potty mouth.

It’s hard to convey how pervasive this notion is. Some of these books are as obsessed with her supposed coarseness as they are with Travelgate, Benghazi, Vince Foster and missing emails. In Edward Klein’s “Guilty as Sin,” which came out last week, roughly two-thirds of the anonymously sourced quotations attributed to Mrs. Clinton are salted with obscenities. It’s enough to make you wonder if the woman has David Milch on monthly retainer, generating her dialogue.

In light of the recently leaked audiotape of Donald J. Trump talking to Billy Bush of “Access Hollywood,” this fixation with Mrs. Clinton’s language makes for a uniquely peculiar reading experience. Mr. Trump’s comments weren’t just foul in style, but in content: He declared that his celebrity allowed him to grab attractive women by the genitals (I am paraphrasing here, but for the four Martians who haven’t heard it, let’s just say he wasn’t delicate about his choice of terms); he used the F-word as a verb, and not in the sense of gaslighting someone or telling a menace to buzz off.

Yet Mr. Trump’s supporters, as we’ve seen, do not care if he is a vulgarian. That, arguably, is precisely what they admire about him — that he says what he thinks, that political correctness gives him a rash. His words were simply “locker room talk,” the muscular flourishes of an alpha male. But the prospect of a blaspheming Hillary Clinton is clearly repulsive to those who despise her. What is it about female profanity — or her possible profanity specifically — that’s such a potent signifier? What is it a conservative shorthand for? Because the text here is not subtle.