Mueller's probe and Sessions' recusal have continued to deeply anger Trump, who raged repeatedly against Sessions on Twitter.
The president has repeatedly called Mueller's investigation a "witch hunt" and this past weekend called it illegal. Trump has pushed back against the conclusion reached by U.S. intelligence agencies that Russia interfered with the election at all.
Sessions was forced out by Trump in early November. Sessions' chief of staff, Matt Whitaker, took over running the Justice Department as acting attorney general.
Whitaker did not recuse himself from overseeing Mueller's investigation despite a Justice Department ethics official recommending that he do so because of his past criticism of Mueller's probes.
There has been widespread speculation that Mueller is winding down at least one part of his investigation, and that he soon will submit a report on his work to the Justice Department.
That speculation, in turn, has led to demands by Democrats that Mueller's report be given to Congress and made public.
During his confirmation hearing in January, Barr said, "I believe it is vitally important that the special counsel be allowed to complete his investigation."
"I also believe it is very important that the public and Congress be informed of the results of the Special Counsel's work. For that reason, my goal will be to provide as much transparency as I can consistent with the law," Barr said.
"I can assure you that, where judgments are to be made by me, I will make those judgments based solely on the law and will let no personal, political or other improper interests influence my decisions."