The Justice Department declined CNBC's request for comment on the president's tweet. The White House did not immediately provide comment on Trump's tweet about Sessions.
Quoting conservatives and Trump-supporting personalities from Fox News Channel, the president endorsed the view that Peter Strzok, an ex-member of Mueller's team, should be "criminally investigated." Strzok was fired from the FBI on Monday over anti-Trump texts.
"The whole thing ... should be shut down," Trump tweeted, quoting Tom Fitton, the president of conservative legal activist group Judicial Watch.
Just after 9 a.m. ET, the president suggested that the probe should be investigating his Democratic rival from 2016, Hillary Clinton. "Why aren't these angry and conflicted Democrats instead looking at Crooked Hillary?" Trump tweeted.
Trump has often and inaccurately referred to Mueller's team as consisting of strictly Democrats. Mueller himself is a Republican. He was named special counsel by Deputy Attorney General Rod Rosenstein, a Republican and a Trump appointee.
The president also focused his ire on current FBI employee Bruce Ohr, whose wife Nellie worked for Fusion GPS, the research firm that produced a dossier alleging salacious connections between Trump and Russia. Bruce Ohr is not a member of Mueller's team.
Amid Trump's latest assault on the investigation of Russian election interference — and potential conspiracy between Trump's campaign and the Kremlin — the president continued his attacks against Omarosa Manigault Newman, a former senior advisor in his administration, calling her a "dog" and a "crazed, crying lowlife."
In the run-up to the release of her White House expose, Manigault Newman has claimed that tapes exist of Trump using racial epithets including the N-word, and has produced other recordings herself. In an MSNBC interview Monday night, she said she would cooperate with the special counsel and hand over the recordings she made if she were contacted again, appearing to confirm that she has been in touch with Mueller's office.
Following his latest salvo against the ex-"Apprentice" star, Trump weighed in on reports of an incident in London being treated as a terror attack.