Through all the controversy, threats and noise surrounding the Trump-Russia investigation, one person has been conspicuously silent: Special Counsel Robert Mueller.

The former FBI director hasn’t uttered a single word in public since he was appointed in May to lead the probe into Russian meddling in the U.S. election despite increasingly combative attacks by Republicans and their allies on the FBI, the Justice Department and the integrity of his probe.

It’s an intentional strategy meant to convey the investigation’s credibility and seriousness in an age of 24-hour noise, amplified by cable news shows and Twitter, according to current and former U.S. officials who know Mueller personally or who have followed his work.

[Trump assails FBI leadership, touts loyalty to police]

Instead of press conferences, Mueller has spoken loudly through a series of indictments and plea deals related to various Trump associates.

Mueller’s approach is unconventional, both in the current political climate and compared with former FBI Director James Comey or previous high-profile public prosecutors like Kenneth Starr, who investigated President Bill Clinton.

The vacuum created by Mueller’s silence has been filled by GOP critics and conservative media charging the investigation is tainted with bias against President Donald Trump. Several House Republicans have called for Mueller to resign, with Matt Gaetz of Florida going to the House floor last week to accuse him of “fishing in the never-Trump aquarium” in choosing prosecutors and FBI agents for his team.

Trump’s lawyers have been trying to build public expectations that Mueller will wrap up soon, but officials say the investigation is ramping up in some ways and is likely to last for most, if not all, of 2018. Areas where the inquiry is accelerating include a close examination of the activities of Trump’s son Donald Jr. and son-in-law Jared Kushner, said two U.S. officials who asked to remain anonymous.

“When you’re a prosecutor, you put your head down, you do your job, and you try as much as you can to ignore the outside world,” said Patrick Cotter, a former U.S. prosecutor who worked in the 1990s with Mueller and others now serving on his team. “This case is not to be tried on cable TV. It’s to be tried in a courtroom.”

Mueller’s approach differs strikingly from Comey’s. As Mueller’s successor leading the FBI, Comey often made controversial public pronouncements. He managed to anger Republicans and Democrats alike over his handling of the federal investigation into Hillary Clinton’s use of a private email server when she was secretary of state.

Trump used Comey’s words and actions against him — especially after he proclaimed during a July 2016 press conference that no prosecutor would pursue criminal charges against Clinton. Trump attacked Comey in tweets and then called him “a showboat” and “grandstander” after firing him in May.

Mueller has avoided those pitfalls. He’s provided no ammunition to fuel Trump’s tweets and given no traction to Republicans who are trying to discredit the investigation of Russian interference in last year’s presidential campaign and whether anyone close to Trump colluded in it.

His approach is also different both legally and personally from that of Starr, who spoke publicly about his investigation into Bill Clinton, said Stanley Twardy, a former U.S. attorney for Connecticut.

The two investigations can’t be readily compared, as Mueller’s is more sweeping and international, said Twardy, now a white-collar criminal defense lawyer at the law firm Day Pitney LLP.

“The way Bob has been doing this is out of the prosecutor’s rule book 101 as to how you handle an investigation,” Twardy said. “There is the court of public opinion, but the court he’s playing in is the district court. And he’s staying there.”

So far, the strategy appears to be working. Republicans have sullied his probe a bit with their attacks, but Mueller has won over key allies who would play instrumental roles should Trump try to force him out.

Deputy Attorney General Rod Rosenstein told House lawmakers during a Dec. 13 hearing that he is fully aware of what Mueller is doing and stands behind him. Rosenstein appointed Mueller and is the only official with the authority to fire him or stop parts of his investigation.

Sen. Chuck Grassley of Iowa, the Republican chairman of the Senate Judiciary Committee, and Senate Majority Whip John Cornyn said in interviews this week that they support Mueller and would oppose efforts to remove him. Republican Sen. Bob Corker of Tennessee said he thinks there would be an “uprising” in the Senate if Mueller were fired. That would be “beyond the pale,” Corker said.

Mueller’s lack of public comment shouldn’t be confused with a failure to communicate, said Cotter, who now heads the white collar criminal defense practice at the law firm Greensfelder, Hemker & Gale, P.C. in Chicago. Mueller is speaking through legal proceedings, Cotter said.

“He’s communicating. He’s sending messages,” Cotter said. “I don’t think his intent is to send a message to the public. It’s to send a message to the people in the investigation, and that’s what he cares about.”

[Mueller’s moves send message to other potential targets: Beware, I’m coming]

To date, Mueller has indicted Trump’s former campaign chairman Paul Manafort and another campaign aide, Rick Gates. The special counsel also secured a guilty plea and cooperation agreement from Trump’s former National Security Adviser Michael Flynn for lying to FBI agents about his contacts with Russians. A low-level foreign policy adviser to the campaign also pleaded guilty to lying to investigators and agreed to cooperate.

Mueller also has kept up a steady back-and-forth with Trump’s lawyers, who have refrained from taking any punches at Mueller. White House lawyer Ty Cobb has repeatedly denied all suggestions that Trump is considering firing Mueller. Cobb has taken a public posture of fully cooperating with the special counsel’s investigation, turning over documents and arranging interviews with White House staff.

But each day is a test of the relationship between Trump’s legal team and Mueller, and that relationship could break down if Mueller probed too deeply into certain areas, such as Trump’s businesses. The president’s lawyers were set to meet with Mueller’s team as early as this week, according to a person familiar with the matter.

Trump took a slight swipe at Mueller this week over a letter his transition lawyer sent to Congress accusing Mueller of inappropriately obtaining emails from the presidential transition period. When asked about the emails, Trump told reporters he was “quite sad to see that. My people were very upset.” But he reiterated that he had no plans to fire Mueller.

The episode prompted one of the few public statements from Mueller’s team in defense of its tactics. “When we have obtained emails in the course of our ongoing criminal investigation, we have secured either the account owner’s consent or appropriate criminal process,” Mueller’s spokesman, Peter Carr, said in an email.

Mueller’s strategy has forced some critics to reorient their attacks, Cotter said. “You can’t stand there with a straight face and say there’s absolutely nothing here” after the indictments and Flynn’s agreement to cooperate, Cotter said.

The new approach by Trump’s allies is to try to delegitimize Mueller’s investigation, such as by arguing members of the team are biased, Cotter said.

While Mueller is a registered Republican, House Republicans have seized on the disclosure that a top FBI agent assigned to the investigation, Peter Strzok, sent anti-Trump texts in personal exchanges with another FBI official in 2016. Mueller removed Strzok from his team over the summer when he learned of the texts.

“It’s a tactical change,” Cotter said. “If you convince people that whatever the investigation comes out with is bad, just because of the people who did it, then you don’t ever have to deal with the facts.”

Cotter doesn’t believe the new tactic will fare any better, or prod Mueller into making a mistake. “I can’t imagine why Mueller and his people would possibly care,” he said. “The bias in law enforcement is always in favor of law enforcement. They don’t like criminals.”

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