I have nothing specific—but if my theory about communications sabotage and other “mistakes” is correct it would have required both state and SS moles to make it happen.
The Deep State method of operation is to reward those who do them big favors—and as you say Shapiro is “in the running” to be a future Democratic presidential candidate.
Imho he would have been the Democrat nominee if the assassination had been successful.
Example: Gerald Ford made his “bones” by marking up the Warren Commission report in his own handwriting—with forensic details that were obviously way beyond his knowledge base.
That was a “secret” until the Warren Commission draft with handwritten notes was released a couple of years ago—Ford could easily have been blackmailed since he proved he was an accessory after the fact.
It is a type of secret “initiation”—a lot like street gangs.
One of their problems (they think, but that could backfire) is how to get rid of Biden. If I were Trump, I would be very suspicious of in-person appearances of Trump and Biden.
Sometimes you have to read between the lines.