That section of the FOIA statute exempts from disclosure "records or information compiled for law enforcement purposes, but only to the extent that the production of such law enforcement records or information (A ) could reasonably be expected to interfere with enforcement proceedings, (B ) would deprive a person of a right to a fair trial or an impartial adjudication, (C ) could reasonably be expected to constitute an unwarranted invasion of personal privacy, (D ) could reasonably be expected to disclose the identity of a confidential source, including a State, local, or foreign agency or authority or any private institution which furnished information on a confidential basis, and, in the case of a record or information compiled by criminal law enforcement authority in the course of a criminal investigation or by an agency conducting a lawful national security intelligence investigation, information furnished by a confidential source, (E ) would disclose techniques and procedures for law enforcement investigations or prosecutions, or would disclose guidelines for law enforcement investigations or prosecutions if such disclosure could reasonably be expected to risk circumvention of the law, or (F ) could reasonably be expected to endanger the life or physical safety of any individual"

My guess is that plan is to force DOJ into publicly acknowledging that they are investigating him.

EXCELLENT !

Trump is well known to use the pejorative “Newscum” and other insulting sobriquets.
It also doesn’t include any use of the term Governor of California or CAGOV, GOVCA, or similar, which could have been used as methods of obscuring the target of investigation(s).
Finally they don’t ask for the code name associated with the investigation(s).