U.S. Attorney John Durham's ongoing probe into potential FBI and Justice Department misconduct in the run-up to the 2016 election through the spring of 2017 has transitioned into a full-fledged criminal investigation, two sources familiar with the investigation told Fox News on Thursday night.

One source added that DOJ Inspector General Michael Horowitz's upcoming report on alleged FBI surveillance abuses against the Trump campaign will shed light on why Durham's probe has become a criminal inquiry. Horowitz announced on Thursday his report would be available to the public soon, with "few" redactions.

The investigation's new status means Durham can subpoena witnesses, file charges, and impanel fact-finding grand juries.

Fox News reported on Tuesday that Durham's probe had expanded significantly based on new evidence uncovered during a recent trip to Rome with Attorney General Bill Barr.

Barr reportedly told embassy officials in Italy that he "needed a conference room to meet high-level Italian security agents where he could be sure no one was listening in."

A source in the Italian Ministry of Justice told The Daily Beast earlier this month that Barr and Durham were played a taped deposition made by Joseph Mifsud, the professor who allegedly told ex-Trump aide George Papadopoulos that the Russians had "dirt" on Hillary Clinton. Mifsud reportedly was explaining to investigators in the deposition why people would want to harm him, and why he needed police protection.

Papadopoulos has suggested he was connected with Mifsud as part of a setup orchestrated by intelligence agencies.

Sources told Fox News that Durham was "very interested" to question former Director of National Intelligence James Clapper and former CIA Director John Brennan, an anti-Trump critic who recently dismissed the idea. The New York Times reported Thursday that Durham's criminal review has prompted some CIA officials to obtain criminal legal counsel in anticipation of being interviewed.

GOP REVEALS NEVER-BEFORE-SEEN STRZOK TEXTS DISCUSSING 'CRESCENDO OF LEAKS'

Brennan and Clapper were at the helm not only when Mifsud spoke to Papadopoulos, but also when an unverified and largely discredited dossier, written by British ex-spy Christopher Steele and funded by the Hillary Clinton campaign and Democratic National Committee, was used to help justify a secret surveillance warrant against former Trump adviser Carter Page in the run-up to the 2016 election. (The Times' reporting on Thursday, which overtly framed Durham's probe as politically tainted without evidence, did not mention the Steele dossier at all.)

The FBI apparently obscured the fact that the Clinton campaign and DNC funded the dossier in its warrant application, telling the secret court only that the dossier was prepared at the behest of an unidentified presidential campaign.

Additionally, in its original FISA application and subsequent renewals, the FBI told the FISA court it "did not believe" Steele was the direct source for a Yahoo News article implicating Page in Russian collusion. Instead, the FBI suggested to the secret court, the September 2016 article by Michael Isikoff was independent corroboration of the dossier. But, London court records showed that contrary to the FBI's assessments, Steele briefed Yahoo News and other reporters in the fall of 2016 at the direction of Fusion GPS.

It has further emerged that Steele had communications with a State Department contact -- which were relayed to the FBI -- in which Steele claimed the Russians were running a "technical/human operation run out of Moscow targeting the election" and that "payments to those recruited are made out of the Russian Consulate in Miami."

There is no Russian consulate in Miami, a fact the State Department official, Deputy Assistant Secretary of State Kathleen Kavalec, emphasized in her notes. And, Steele had suggested his client was "keen" to see his information come to light prior to Election Day.

Kavalec forwarded her notes to the FBI and other government officials several days before the FISA warrant was issued for Page.

Additionally, Special Counsel Robert Mueller was unable to substantiate other key claims in the dossier, including that the Trump campaign employed hackers in the United States, that there was a compromising recording of the president in a hotel room, and that ex-Trump attorney Michael Cohen flew to Prague to build a conspiracy with hackers. Cohen has denied ever heading to Prague, and no public evidence has contradicted that claim.

Nevertheless, in responding to the expanded Durham probe, House Judiciary Committee Chairman Jerry Nadler, D-N.Y., and House Intelligence Committee Chair Adam Schiff, D-Calif., followed the Times' framing and accused the Trump administration of misconduct.

“These reports, if true, raise profound new concerns that the Department of Justice under Attorney General William Barr has lost its independence and become a vehicle for President Trump’s political revenge," they said. “If the Department of Justice may be used as a tool of political retribution, or to help the President with a political narrative for the next election, the rule of law will suffer new and irreparable damage.”

Also on Thursday, top Republicans revealed never-before-seen texts from fired FBI agent Peter Strzok, in which he apparently discussed systemic leaking at the bureau.

DISPUTE ERUPTS AS BRENNAN, COMEY APPEAR TO DISPUTE WHO PUSHED THE STEELE DOSSIER

Senate Homeland Security Committee Chairman Ron Johnson, R-Wis., and Finance Committee Chairman Chuck Grassley, R-Iowa, revealed the texts in a letter to the Intelligence Community Inspector General (ICIG) requesting an update on whether the FBI's apparent leaks to the media were being probed.

The senators pushed to know whether the ICIG was looking into Strzok's email to FBI colleagues on April 13, 2017, when he wrote that an unidentified "agency" might be the "source of some of the leaks" to the media that he'd been seeing.

READ THE FULL LETTER TO ATKINSON, INCLUDING THE NEWLY RELEASED STRZOK TEXTS

"I'm beginning to think the agency got info a lot earlier than we thought and hasn't shared it completely with us," Strzok wrote, according to documents that the senators included in their letter to the ICIG. "Might explain all these weird/seemingly incorrect leads all these media folks have. Would also highlight agency as a source of some of the leaks."

The senators also asked why Strzok texted bureau colleague Lisa Page on Dec. 15, 2016: "Think our sisters have begun leaking like mad. Scorned and worried and political, they're kicking in to overdrive."

"What are they worried about, and what are they kicking into 'overdrive?' Johnson and Grassley wrote. "Who are the 'sisters,' and what does it mean to say that the 'sisters have [been] leaking like mad'?"

In a June 6, 2017 email to Page, Strzok mused, "Think there will be a crescendo of leaks/articles leading up to Thurs."

And, a Dec. 13, 2016 text message apparently showed Strzok trying to set up a Skype meeting with a reporter. "Text from reporter: retrieving my password for Skype," he wrote.

Then, on April 6, 2017, Strzok wrote to senior FBI leadership to complain about a New York Times article entitled, "C.I.A. Had Evidence of Russian Effort to Help Trump Earlier Than Believed," claiming it painted the FBI in an unfavorable light and got key facts wrong.

"Mike, below is inaccurate, favors the CIA at the expense of the FBI in particular, and is at odds with what Apuzzo and Goldman know," Strzok wrote. "Most importantly, it's at odds with the D's [FBI Director's] recent public testimony that we've been looking at links (which necessarily imply favoring Trump) since July '16."

Strzok specifically objected to the Times' reporting that the CIA's briefings with lawmakers "indicate that intelligence officials had evidence of Russia’s intentions to help Mr. Trump much earlier in the presidential campaign than previously thought," and "reveal a critical split last summer between the C.I.A. and counterparts at the F.B.I., where a number of senior officials continued to believe through last fall that Russia’s cyberattacks were aimed primarily at disrupting America’s political system, and not at getting Mr. Trump elected, according to interviews."

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Horowitz, the DOJ watchdog, faulted the FBI last year for repeated violations of its media communications policy, noting that agents had received gifts from reporters and leaked regularly and brazenly -- even from phones at FBI headquarters in Washington, D.C.

Fox News' Jake Gibson contributed to this report.