President Donald Trump flung some of his harshest words yet at Special Counsel Robert S. Mueller III on Tuesday, calling the former FBI director who is investigating his 2016 campaign “a conflicted prosecutor gone rogue.”

Trump’s latest broadside against Mueller prompted swift pushback from a former senior Obama administration official, John Brennan, who shot back his stance that Trump’s “feelings of inferiority, insecurity, vulnerability, and culpability are loud & clear.”

The president began by again labeling Mueller’s probe a “Phony Witch Hunt” and accusing him of “only looking at one side, not the other.” That is a reference to Trump’s contention of Democratic collusion in 2016 with Russia, rather than his own campaign, as well as 2016 Democratic presidential nominee Hillary Clinton’s use of a private email server when she was secretary of state.

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“Wait until it comes out how horribly & viciously they are treating people, ruining lives for them refusing to lie,” the president wrote, referring to former campaign associates who have pleaded guilty or been indicted by Mueller’s team or other federal prosecutors.

Trump, who has faced charges of undermining the Justice Department and longstanding legal traditions, fired off two more tweets accusing Mueller of “doing TREMENDOUS damage to our Criminal Justice System” and predicting “Heroes will come of this, and it won’t be Mueller and his…….terrible Gang of Angry Democrats.”

The Phony Witch Hunt continues, but Mueller and his gang of Angry Dems are only looking at one side, not the other. Wait until it comes out how horribly & viciously they are treating people, ruining lives for them refusing to lie. Mueller is a conflicted prosecutor gone rogue….

— Donald J. Trump (@realDonaldTrump) November 27, 2018

….The Fake News Media builds Bob Mueller up as a Saint, when in actuality he is the exact opposite. He is doing TREMENDOUS damage to our Criminal Justice System, where he is only looking at one side and not the other. Heroes will come of this, and it won’t be Mueller and his…

— Donald J. Trump (@realDonaldTrump) November 27, 2018

….terrible Gang of Angry Democrats. Look at their past, and look where they come from. The now $30,000,000 Witch Hunt continues and they’ve got nothing but ruined lives. Where is the Server? Let these terrible people go back to the Clinton Foundation and “Justice” Department!

— Donald J. Trump (@realDonaldTrump) November 27, 2018

(Fact Check: Mueller was first appointed FBI director by GOP President George W. Bush and was appointed special counsel by former Attorney General Jeff Sessions, once a conservative Republican senator from deep-red Alabama.)

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Trump contended Mueller, who has yet to release a final report — or reports — as his probe continues, has “nothing but ruined lives” to show for his months of work.

Brennan, who was CIA director under former President Barack Obama, fired back a few minutes later.

“Your feelings of inferiority, insecurity, vulnerability, and culpability are loud & clear,” he said in a tweet of his own directed at Trump, adding the U.S. president reminds him of “how many corrupt authoritarian leaders abroad behaved before they were deposed.”

Your feelings of inferiority, insecurity, vulnerability, and culpability are loud & clear. You remind me of how many corrupt authoritarian leaders abroad behaved before they were deposed. Bob Mueller’s name will be revered in the annals of U.S. history; your name will be scorned. https://t.co/aYnYetwJV1

— John O. Brennan (@JohnBrennan) November 27, 2018

Some of Trump’s personal and White House legal advisers long cautioned him to avoid publicly criticizing Mueller. But in recent weeks, Trump has discarded that advice and gone right after the special counsel.