The government can waive Sovereign Immunity in certain circumstances - i.e. the government agrees to be sued.
In Mueller’s case not clear, but the stretch to get him on a claim is a lot shorter then trying to claim that a personal payment to a female shakedown artist is a campaign contribution.
https://legal-dictionary.thefreedictionary.com/Sovereign+Immunity
Prosecutors enjoy absolute immunity for their prosecutorial functions. But not their administrative functions.
Leaking to the press, i.e., public relations, seems to be an administrative function. No?
Too late to review the caselaw.
The mind boggling part this to me is there is more on Trumps accusers for trying to frame him, than on Trump himself.
This should have been obvious to Mueller before he became special counsel.