Attorney General Jeff Sessions told congressional leaders on Thursday that he has elected not to appoint a special counsel to investigate allegations that the FBI misused its surveillance powers, in a move that could potentially further alienate the nation’s top law enforcement official from President Donald Trump.

In a letter addressed to the chairs of the Senate Judiciary Committee, the House Judiciary Committee and the House Oversight Committee, Sessions said that he was bound by Justice Department regulations allowing for the appointment of a special counsel under “only the most ‘extraordinary circumstances,’” and has therefore elected instead to task a U.S. attorney with overseeing the review instead.

“In high-profile circumstances involving other politically sensitive matters, it has been more common to make special arrangements within the Department to ensure that actual or apparent conflicts can be avoided,” Sessions said in the letter. Only if “the public interest would be served by removing a large degree of responsibility… from the Department of Justice,” Sessions continued, would he consider appointing a special counsel to conduct the investigation.

That determination will be made, in part, by the career DOJ official Sessions has put in charge of the investigation. U.S. Attorney John W. Huber of Utah, a career prosecutor who has served under both Republican and Democratic presidents, has been tasked with leading the review. In the letter, Sessions noted that Huber is “an experienced federal prosecutor who was twice confirmed unanimously by the Senate.”

Asked when exactly Huber had begun evaluating issues raised by the committees addressed in the letter, Department of Justice spokesperson Sarah Isgur Flores told The Daily Beast only that Huber started “in advance of the Nov. 13th letter.” In that November letter, sent by Assistant Attorney General Stephen Boyd to the House Judiciary Committee, congressional leaders were told that “senior prosecutors” reporting directly to Sessions “will make recommendations as to whether any matters not currently under investigation should be opened.”

Congressional conservatives have pushed for a review of the FBI’s response to Hillary Clinton’s handling of classified information, the FBI’s use of Foreign Intelligence Surveillance Court warrants to monitor former Trump campaign aide Carter Page, and allegations that a foundation linked to a Canadian uranium mining company donated to the Clinton Foundation in order to facilitate government approval of that firm’s sale to a Russian nuclear energy corporation.

Despite Sessions’ professed confidence “that Mr. Huber’s review will include a full, complete and objective evaluation of these matters in a manner that is consistent with the law and facts,” the decision to hold off on appointing a Robert Mueller-type special counsel to investigate the FBI and Clinton will likely frustrate some Republican lawmakers—as well as Sessions’ boss.

“Why is A.G. Jeff Sessions asking the Inspector General to investigate potentially massive FISA abuse,” President Trump tweeted last month, upon news that Sessions had also move to enlist the Department of Justice’s inspector general to look into potential FISA abuses. “Will take forever, has no prosecutorial power and already late with reports on Comey etc. Isn’t the I.G. an Obama guy? Why not use Justice Department lawyers? DISGRACEFUL!”

The White House did not immediately respond to a request regarding Sessions’ decision to not appoint a special counsel.