This sounds like yet another attempt by the corrupt FBI to taunt Trump into firing someone so the rats can than scream Trump is interfering in the endless investigation in search of a crime.
Yes, it's like a chess move where your attacking piece is protected by other pieces. However, the game may have another level that even RR doesn't understand.
I think it's likely Justice Kennedy made a deal with Trump to have himself replaced with Kavanaugh if he agreed to retire while Trump is POTUS. Trump may not want Kavanaugh on SCOTUS and is secretly hoping for something to float to the surface which takes Kavanaugh out of consideration.
If that happens Trump can honestly claim he upheld his end of the deal with Kennedy, but that weasel RR came along and dug up dirt, so whadda gonna do, that's life. Then he can nominate his real choice for the court.