Attorney General William P. Barr has taken an interest in a mysterious European professor whose conversation with an adviser to President Trump’s 2016 campaign helped launch the FBI investigation into possible coordination with Russia — and who has since become the focal point of an unproven conservative theory that the entire inquiry was a setup, people familiar with the matter said.

Those involved in the FBI investigation said they are mystified by the attorney general’s activities and interest in the professor, Joseph Mifsud, and they suspect that Barr might be using Justice Department resources to validate conjecture that Mifsud was deployed against a Trump adviser by Western intelligence to manufacture a basis to investigate the campaign.

“It just seems like they’re doing everything they can to delegitimize the origins of that investigation,” said one person involved with the Russia probe, who, like others, spoke on the condition of anonymity to discuss the politically sensitive matter that is still being reviewed. “I just don’t think there’s any real basis to disparage it.”

But Barr’s inquiry has heartened Trump and his conservative allies. Trump, who at times has inquired about the origins of the Russia investigation and the professor in particular, has bragged that Barr will get to the bottom of the case and is doing a good job as the country’s top law enforcement official, a White House official said.

Barr’s defenders assert that he is exploring what he views as possible problems.

“He’s not a conspiracy theorist. He’s a realist,” said George Terwilliger, a former deputy attorney general and longtime friend of Barr’s. “And I’m confident that if he has a concern that justifies his personal involvement, it’s based on fact, not conjecture.”

Over the past three years, Trump officials have often defended the president initially, only to walk back their statements later. (JM Rieger/The Washington Post)

A Justice Department spokeswoman declined to comment.

Unproven or vague allegations about impropriety in the origins of the FBI’s Russia probe have long been passed between Trump, his conservative allies on Capitol Hill and the conservative media ecosystem — with the country’s top law enforcement official and conservative lawmakers sometimes helping to fuel them.

Sen. Lindsey O. Graham (R-S.C.) wrote in recent days to Australian, Italian and British officials, asking them to cooperate in Barr’s review of the Russia investigation and asserting that the attorney general was “simply doing his job.” Graham said in an interview that he expected Mifsud to be a significant part of the investigation.

“He’s a curious character in this whole deal, and we need to know more about him,” Graham said, adding that he had not talked to Barr about the matter.

“Whatever Barr finds is fine with me,” he said. “If there’s nothing there, there is nothing there. I trust him.”

Barr has never spoken specifically about his view on the theories surrounding Mifsud, though people familiar with his thinking say he is interested in the professor and the broader work of the U.S. intelligence community surrounding the Trump campaign. The Washington Post recently reported that Barr had been traveling abroad — to the United Kingdom and Italy, in particular — to ask his foreign counterparts to aid in the Justice Department’s review of the matter.

Barr has long harbored suspicions about the Russia probe, which began before the 2016 election and was later overtaken by then-special counsel Robert S. Mueller III after Trump fired FBI Director James B. Comey early in his tenure as president. Even before he was nominated, Barr had written a letter to Justice Department leaders asserting that the special counsel’s theory of how Trump might have obstructed justice in the Russia probe seemed “fatally misconceived.” At a Senate Appropriations Committee hearing in April, Barr said he believed “spying did occur” against the Trump campaign — using a term some feel has a negative connotation, and one which FBI Director Christopher A. Wray later said he would not use.

In May, it was revealed that Barr had assigned U.S. Attorney John H. Durham to determine if the U.S. government’s “intelligence collection activities” related to the Trump campaign were “lawful and appropriate.” Barr told CBS News that month that some of the facts he had learned “don’t hang together with the official explanations of what happened,” but he declined to be more specific.

“That’s all I really will say,” Barr said. “Things are just not jiving.”

The unproven theory about Mifsud is that the Maltese professor was working to set up the Trump campaign. Mifsud was undeniably critical to the FBI’s decision to open an investigation. He boasted to Trump campaign adviser George Papadopoulos about having “dirt” on Hillary Clinton in the form of “thousands of emails” — before Russia’s hacking of Democrats was publicly known. When the FBI learned of that conversation some months later, it opened a case.

Mueller’s team wrote that Mifsud “had connections to Russia,” and Comey has described him more bluntly as a “Russian agent.”

James Baker, who was the FBI’s general counsel when the bureau opened the counterintelligence probe, defended the investigation. “It’s critically important that the American people have confidence in the intelligence community,” he said. “I’m confident that there was no attempted coup and that nothing was done for political reasons.”

Baker said that after Durham was appointed, he contacted the prosecutor and offered to cooperate with the review. Durham has yet to contact Baker, Baker said.

David Laufman, a former Justice Department counterintelligence official involved in the early stages of the Russia investigation, said on Twitter that Barr’s “spearheading of a Justice Dept. investigation to pursue conspiracy theories about the 2016 election is cause for alarm at the hijacking of a great institution to vindicate partisan political grievances.”

Mifsud was never accused of crimes and last surfaced two years ago for an interview with a reporter in Italy. That has fueled speculation, particularly from those who want to discredit the Russia probe, that he is not what the FBI says he is.

Trump’s personal attorney Rudolph W. Giuliani told The Washington Post that he was interested in Mifsud because it “seems to me it was a counterintelligence setup . . . a rather typical CIA plot to create a basis for the investigation.”

Giuliani noted that he had not talked to Barr or Durham about the matter. A person familiar with Barr’s thinking said Barr has questioned the wisdom of Giuliani’s attempts to get foreign nations, especially Ukraine, to pursue investigations of interest to the president because Giuliani is operating outside normal government channels.

Papadopoulos, who pleaded guilty to lying to the FBI about his interactions with Mifsud, has tweeted that Mifsud was “an Italian intelligence asset who the CIA weaponized.”

Caroline Polisi, a lawyer for Papadopoulos, declined to say whether he has been contacted by Durham or Barr as part of the Justice Department’s review.

Attempts to locate Mifsud were unsuccessful. Stephan Roh, a Swiss lawyer who purports to represent him, has called accusations that Mifsud was a Russian asset “defamatory.”

In Roh’s 2018 book, which postulates that Mifsud was working with Western intelligence, Roh indicated that he interviewed Mifsud about his interactions with Papadopoulos that same month.

Roh did not respond to questions about when he was last in contact with the professor or where he is located. In an email, he declined to comment on any interactions Mifsud has had with the Justice Department “or if there were any.”

According to a former Italian government official, Barr first met with Gennaro Vecchione, the head of Italy’s Security Intelligence Department, on Aug. 15, essentially to establish contact, and returned Sept. 27 for a second meeting with the heads of Italy’s domestic and foreign intelligence services.

Barr, the official said, “asked if Italian intelligence knew anything about Mifsud and if the Italians were aware of his role” in the Russia investigation “in terms of being involved in Italian intelligence itself or if he was politically tied with Italian political leaders allied with the Democrats.” The Italians, the official said, “explained that there is no involvement by the Italian intelligence services in this — and the fact that we don’t have any evidence of this plot.”

“They confirmed no connections, no activities, no interference,” the official said.

The Justice Department inspector general is also examining aspects of the FBI’s Russia probe, but some who have been questioned in it said that Mifsud has not seemed to be a key focus of investigators.

Barr’s critics say his efforts to investigate the investigators are meant to placate Trump — even if that means casting aspersions on U.S. law enforcement and intelligence agencies.

Trump had virtually no relationship with Barr when he chose him to be attorney general in late 2018, and conservative and liberal lawyers alike hoped that Barr might restore independence to the Justice Department that they felt had been eroded in the first years of Trump’s presidency. Barr had been attorney general before, in the George H.W. Bush administration, and was widely respected in conservative legal circles.

Some analysts said Barr disappointed quickly. His characterization of the Mueller report, they noted, hewed closely to Trump’s favored talking point — no collusion, no obstruction — and Mueller felt it so misleading that he complained in a letter that the attorney general “did not fully capture the context, nature, and substance” of the special counsel’s work.

“Like most Republican lawyers or most lawyers in Washington, I expected that Bill Barr would be a very by-the-book sort of attorney general, especially since he had done it before and certainly knows the job,” said Greg Brower, a former U.S. attorney now in private practice at Brownstein Hyatt Farber Schreck. “Unfortunately, many people in town now think he is playing politics, or he’s running the department in a way that he’s too political.”

Other analysts, though, noted that Barr had essentially telegraphed the type of attorney general he would be before he was nominated. In addition to writing a memo critical of Mueller, Barr had opined to a New York Times reporter in 2017 that the basis for investigating alleged wrongdoing by the Clinton Foundation, as well as the controversial sale of a uranium company to Russia while Hillary Clinton was secretary of state, was stronger than the basis for launching the Russia investigation.

“I have long believed that the predicate for investigating the uranium deal, as well as the [Clinton] Foundation, is far stronger than any basis for investigating so-called ‘collusion,’ ” Barr wrote.

Matthew Miller, a Justice Department spokesman when Eric H. Holder Jr. was attorney general, said that when he first saw Barr’s comment, “I thought, this is someone who’s had his brain warped by a couple decades of Fox News, and that’s not the type of person that should be leading the Justice Department.”

“I think Trump basically got what he wanted at the Justice Department — which is someone that would define his job as protecting the president first and foremost,” said Miller, who is an analyst for MSNBC.

Terwilliger, the former deputy attorney general, disputed that assessment, saying Barr “remains as straight an arrow and middle of the road as he can be.”

“If he thinks that there was malfeasance in some aspect of the way the government operated in a way that was designed to hurt the presidency, I think he has every right — indeed, a responsibility — to uncover that,” Terwilliger said.

Barr’s critics and defenders alike note that he has long believed in a strong executive branch, and that is likely to inform some of his interest in protecting Trump and the office he holds.

“When you pair someone with that view of executive authority with this particular president,” said Matt Axelrod, a Justice Department official when Loretta E. Lynch was attorney general, “it’s a recipe for disaster.”

Barr’s defenders, though, note that he has generally enjoyed a good reputation and — given this job might be his last — he is unlikely to want to ruin it over causes in which he doesn’t believe.

“Throughout his career, both in public life and in the corporate world, he’s always been viewed as an individual of tremendous integrity and honesty and always beyond reproach,” said Leonard Leo, executive vice president of the conservative Federalist Society legal organization. “I just don’t see him — at the twilight of his career, given everything he’s done, and given his faith-based and spiritual life — coming off the rails at this point.”

Ellen Nakashima contributed to this report.