In modern presidential campaigns, unsubstantiated conspiracy theories about pedophilia are now almost as routine as stump speeches, poll results and televised debates.
In 2016, Democrats' imagined penchant for child predation was manifested in the made-up charge that Hillary Clinton presided over a child sex-trafficking ring. Adherents of this fiction spun an elaborate online fantasy that the presidential candidate - along with her husband, former President Bill Clinton, and other prominent Democrats - was running such an enterprise from a nonexistent network of tunnels underneath a real-life pizza joint in Washington, D.C.
Clinton lost the election, but the fabricated charge that a secret cabal of pedophiles rules the Democratic Party remained a central feature of the QAnon conspiracy theory. Its adherents are allied with President Donald Trump, the man they see as leading the charge against these "deep state" elites.
Now similar fictions are being aimed at Joe Biden, this year's Democratic presidential nominee.
The hashtag #PedoBiden has been on the rise in recent months, and Trump gave it a boost by retweeting a video from an anonymous Twitter account that purported to show Biden in the act. The issue came up in Trump's Thursday night town hall, when the president refused to repudiate QAnon and commended its adherents for being "strongly against pedophilia."
In fact, the woman shown with Biden's hands on her shoulders and his mouth to her ear was in her 40s at the time, and she has denounced the smear campaign against the former vice president. But Trump's elevation of the false pedophilia claim ensures its place in the firmament of conspiratorial fabrications.
It also raises questions. Why do conspiracy theories built around pedophilia hold sway for so many? And why do their adherents tend to favor Trump?
Of all the epithets hurled by politicians through history, an accusation of child sexual abuse strikes particularly deep chords, experts say.
Those chords resonate across the political spectrum. They rivet attention by evoking vulnerable children. They engage one of humankind's most primitive and powerful emotions - disgust. And they place members of this evil cabal in a class beyond redemption.
Like all conspiracy theories with legs, this one draws credibility from evil deeds we know to be real. After all, the cases against Catholic clergy, the financier Jeffrey Epstein and disgraced Olympic gymnastics team doctor Larry Nassar all suggest that child sexual abuse may be perpetrated by fellow citizens we may once have trusted and admired.