Given the circumstances, one can only conclude that the veiled references in the letter are to the obvious thing:
sex with underage girls.
Rape.
Pedophilia.
The President of the United States is a pedophile.
It is common, or at least it used to be, to portray Trump as a unique irruption into the American political scene:
uniquely crass, uniquely rapey, uniquely popular.
In that frame of mind, one might dismiss Trump's association with Epstein as yet another uniquely Trumpian deformity.
What if it isn't?
What if the connection between reactionary MAGA politics and the sexual abuse of children is deeper than we want to admit?
The name for this idea is pedocon theory.
https://www.liberalcurrents.com/we-need-to-talk-about-pedocon-theory/