All his life, the Vietnam War Marine veteran has lived out a code of discreet personal values -- elevating government service, the rule of law and respect for the chain of command.

But now, the uproar triggered in the wake of Mueller's Russia investigation raises the question of whether his time-honored methods have left him vulnerable to exploitation in a new political era of hyper-partisanship and self-aggrandizing.

And the discord is increasing calls for Mueller to break his silence in the most public way -- in hearings being demanded by House Democrats , which would become one of the most hotly anticipated congressional appearances in years.

Mueller's habitual reticence earned him a reputation for integrity that made him the ideal choice for the radioactive mission of investigating a sitting president's campaign.

But in retrospect, it let others -- who do not necessarily follow his blueprint for life -- tell his story themselves.

That left the long-held assumption that Mueller's words in his report would speak for themselves undermined -- to the political advantage of President Donald Trump, who is claiming blanket exoneration that the report does not confer.

'Blessed' to serve

Even as FBI director, Mueller never sought the limelight, was reluctant to promote himself and avoided the press if he could. His regular appearances on Capitol Hill were noted for their economy of information and discretion.

Mueller always let his work -- his indictments, his reports and the conduct of the subordinates he schooled -- do the talking in a career in which he mostly chose to swap the rewards of corporate law for government work.

"I am blessed and exceptionally fortunate to do what I love doing and that opportunity comes in the form of service," Mueller told students at his old prep school, St Paul's, in 2004.

It was that obligation that brought him back to the Justice Department again, when he was named special counsel in May 2017, after his successor at the FBI, James Comey, was fired.

Soon, Mueller, a lifelong Republican, was at the center of a political firestorm.

He ignored the inaccurate daily torrent of attacks from Trump and his propagandists in conservative media for two years.

The decision kept the investigation from being drawn into the political crossfire. But it also gave the Trump machine an open field to create a toxic atmosphere around Mueller's probe and to insulate the President among his vital political base.

Subsequent events raise the question of whether Mueller's courtly and quiet approach is a poor fit for a time when a President tweets and spreads unfounded conspiracy theories.

For the last two years, Mueller has been a ghostly presence, dominating Washington's waking hours, but never heard.

He didn't give interviews. He didn't talk to door-stepping reporters. He didn't roll out his indictments himself -- he left that to Deputy Attorney General Rod Rosenstein. His big cases were conducted in court by subordinates. Mueller's team could have spoken after the conviction of Trump's former campaign chairman Paul Manafort. They didn't, though they left a rich trail of "speaking indictments" that details the Russian election interference operation and misconduct by associates of Trump's.

The only public words Mueller uttered related to the investigation over its near two-year span was the phrase "no comment" four times when he was approached by an NBC reporter outside church last month.

One of the few occasions when Mueller's spokesman entered the fray was when he knocked back a BuzzFeed report this year that accused Trump of suborning perjury.

And when he was done, Mueller turned over his findings to his superiors and didn't hold a news conference or show up at Barr's public unveiling of the report last month.

Rules governing Mueller's appointment do not require him to talk to the American people. But there are mechanisms for him to do so should he want to.

There was, however, the cautionary spectacle of Comey's news conference after he decided to make no indictments in the Clinton email probe, which drew the bureau into a damaging political imbroglio it has yet to escape.

In some ways, Mueller couldn't win. But politics abhors a vacuum.

Barr and the White House fill the vacuum

Aggressive interventions by Barr and the White House created an unstoppable narrative of exoneration that dulled the political impact of an investigation that -- if it did not find prosecutable crimes -- sketched a devastating picture of lies, apparent abuses of power and duplicity in the West Wing.

Mueller's reclusiveness and deference to authority are what make his letter to Barr questioning the attorney general's framing of the special counsel report so extraordinary.

"There is now public confusion about critical aspects of the results of our investigation," Mueller wrote in the letter dated March 27, 2019.

"This threatens to undermine a central purpose for which the department appointed the special counsel: to assure full public confidence in the outcome of the investigations."

In a way, this was Mueller breaking his silence. He leveraged his reputation -- and by putting his arguments so forcefully and on paper, he knew they would eventually emerge. It was an extraordinary step from a man known for his deference to authority.

Democrats now want a public accounting from Mueller -- especially after Barr's contentious appearance before the Senate Judiciary Committee on Wednesday.

Odd friendship

Barr and Mueller, two titans of Washington's legal elite, have known each other for decades, and have always struck a contrast. The former FBI chief is less partisan. Barr courted controversy in a first term as attorney general in the George H.W. Bush administration.

The first sign of cracks in their odd friendship came with an unsolicited letter to the Justice Department in 2018 in which Barr, though admitting he had not seen Mueller's evidence, took aim at his theory of obstruction as "fatally misconceived."

The letter, given what happened next, is often seen as an audition by Barr for the job of then-Attorney General Jeff Sessions.

By the time of his confirmation hearing, in January, Barr was painting himself as the ideal person to pilot Mueller's report to a sound landing.

"I have known Bob Mueller personally and professionally for 30 years," he said. "We worked closely together throughout my previous tenure at the Department of Justice under President Bush. We've been friends since."

It would not be a surprise if that friendship is under strain -- though Barr did live up to his promise to publicly release the Mueller report, albeit in a redacted version.

Barr is now pulling rank after making sure that his spin on Mueller's work -- particularly on the special counsel's not making a decision on whether Trump had obstructed justice -- became the first and dominant assessment.

"Bob Mueller is the equivalent of a US attorney. He was executing the powers of the attorney general, subject to the supervision of the attorney general," Barr said Wednesday.

"His work concluded when he sent his work to the attorney general. At that point, it was my baby, and I was making a decision as to whether or not to make it public," he added.

Barr also seemed irritated by Mueller's letter, which leaked on the eve of his Senate Judiciary Committee appearance.

"You know, the letter's a bit snitty, and I think it was probably written by one of his staff people," Barr said.

The great irony of Barr's appearance is that the uproar he fomented makes it almost inevitable that Mueller will be called to testify in the most public of forums.

Though Senate Republicans are ready to move on, House Democrats are calling with fresh urgency for Mueller to meet lawmakers.

Barr said on Wednesday that he would have no objection to Mueller testifying. But it's possible that pressure from the White House and another twist in the drama over the special counsel could mean there are more fights to come before such an appearance takes place.