To understand what's going on here, I'll attach a page from Mario Puzo's The Godfather.
Recall that the GOP made a big deal at the hearing that no fact witness ever heard Trump say directly that he was withholding security aid for an investigation into the Bidens. . .
Here it's reported that Giuliani is coming right out and saying that Trump was the one pushing for the investigations.
The consigliere is pointing his finger upward, to the top.
Giuliani won't go quietly under that bus.
Giuliani's lawyer said it was a 'joke.' Yeah, right [I wrote that in the sarcasm font]
Why the threat?
Because Trump actually doesn't have the Godfather's power.