Jason Foster, chief investigative counsel to the Senate Judiciary Committee, fits a classic Washington profile: A powerful, mostly unknown force at the center of some of the most consequential battles on Capitol Hill.

For the last year, Foster — empowered by his boss, Sen. Charles Grassley, R-Iowa, the committee’s chairman — has been the behind-the-scenes architect of an assault on the FBI, and most centrally its role in special counsel Robert Mueller’s investigation of possible collusion between the Trump campaign and Russia, according to interviews with current and former congressional aides, federal law enforcement officials and others.

With Foster in charge of his oversight work, Grassley has openly speculated about whether former FBI director James Comey leaked classified information as Comey raised alarms about President Donald Trump’s possible interference in the Russia probe. Grassley and the other Republicans on the committee have questioned the impartiality of a former member of Mueller’s team, cast doubt on the credibility of the FBI’s secret court application for permission to surveil a Trump campaign associate and called for a second special counsel to investigate matters related to Hillary Clinton. A firm that conducted opposition research on Trump has made clear in court it believes Grassley’s committee, with Foster as its lead investigator, had leaked sensitive information about its business.

Most recently, many of those interviewed by ProPublica said, Foster engineered Grassley’s highly unusual public announcement asking federal authorities to consider criminal charges against Christopher Steele, the ex-British spy who compiled the dossier warning of possible collusion between the Trump campaign and the Kremlin.

For Foster’s critics, and they include Republicans as well as Democrats, his provocative work on the Trump-Russia investigation is just the latest chapter in the career of a partisan combatant willing to discard norms and indulge in conspiratorial thinking as he pursues investigations favorable to Republicans.

Foster — who cut his teeth on Capitol Hill working on the staff of former Rep. Dan Burton, R-Ind., who fueled the theory of foul play in a Clinton aide’s suicide and called for required AIDS testing for all Americans — drew the ire of many for his role in various Judiciary Committee investigations of the Obama administration.

“That’s the way it seemed to go every time with Jason, conspiracy to the point it was ridiculous,” said one Democratic aide who had dealt with Foster. The aide was one of several interviewed by ProPublica, Democrat and Republican, who would not be identified because they were not authorized to speak publicly about the inner workings of Congress.

Foster’s career, including his work on the committee’s Russia investigation, has caught the attention of the Trump administration. Foster has twice been approached about a possible job, an inspector general role, with the administration, a situation that some say should have required his recusal from work on the collusion inquiry.

Foster, 46, would not respond to questions about his work on the committee, and Grassley’s office said its policy was not to comment on specific claims about individual staffers.

But the office offered a broad defense of both Foster and what it regards as the committee’s efforts to aggressively investigate the FBI’s handling of the Trump-Russia probe. The office said Grassley has moved to examine potential misdeeds by Trump and his campaign and would be willing to do so even more vigorously if Democrats would agree to investigate the Obama administration, Hillary Clinton and the firm that produced the Trump-Russia dossier.

Foster has admirers beyond his own office. Some of those interviewed by ProPublica, including several suggested by Foster himself, describe him as a fierce and detail-oriented investigator who is protective of whistleblowers who come to the committee looking to tell their stories. His tough approach with the FBI, they said, long predated the Trump-Russia investigation and he has been willing to take on Republican administrations.

“He isn’t especially deferential but he’s fair,” Hannibal Kemerer, a former judiciary aide, said of Foster’s style. “If he should retire or resign, nobody from the FBI is going to throw him a party. He’s not in it to make friends.”

In examining Foster’s role in the committee’s Trump-Russia investigation, ProPublica discovered that a decade ago he had written an anonymous blog, using the handle “extremist.” The posts by Foster, who was then working for Grassley on the Senate Finance Committee, made clear he was some sort of D.C. insider, and he came across as a knowing observer as the country navigated the thorny political fights of the Bush and Obama eras.

But there were also plenty of times “extremist” lived up to his chosen name.

He warned of an Islamic takeover. He wrote that homosexuality was akin to incest. He questioned whether waterboarding really amounted to torture. He derided Obama’s proposal to negotiate with the Taliban, and was particularly galled that the president doing so had the middle name Hussein. Liberals? They were anti-American.

He even mused about whether Sen. Joseph McCarthy, condemned as a demagogue for his 1950s anti-Communist crusade, should be remembered more kindly.

Foster, in an email sent this week to ProPublica, apologized for his inflammatory posts, saying his “pen name” had been satirical and that his writings had been “stupid and wrong.”

Taylor Foy, a spokesman for Grassley, said the office had no prior knowledge of the blog, but that the beliefs expressed by “extremist” were “not relevant” to Foster’s professional work.

Foy, however, added of Foster’s online opinions, “That persona does not represent the professionalism Jason has exhibited while working on behalf of a broad array of people across the political spectrum, including whistleblowers who face retaliation and discrimination in the workplace.”

None of those ProPublica spoke to about Foster, admirers or critics, were aware of his blogging. Some, upon learning of his posts, said they were completely at odds with the public servant they knew. Others, however, said they were disturbed, but not entirely surprised by his words, given his recent work.

“It’s not a total shock,” a former Republican aide said. “But it went beyond what I expected from the person I knew.”

Foster attended Georgetown Law School, and immediately after finishing went to work on Capitol Hill. He started as a legislative assistant in the House of Representatives, but was quickly tapped to work on Burton’s Oversight and Government Reform Committee.

The Indiana congressman was known for outlandish beliefs: He frequently pushed the theory that vaccines cause autism and was said to avoid soup in restaurants for fear of contracting HIV.

Burton‘s investigations of the Clinton White House were so extreme many mainstream Republicans were repelled. He aggressively pursued the theory that Clinton aide Vince Foster, who committed suicide, had been murdered and that the Clintons may have been involved. Burton reenacted the alleged killing by shooting a melon in his backyard. An expert at a conservative think tank called it all “investigation as farce.”

Foster eventually joined Grassley’s staff in 2005, when Grassley was the top Republican on the Senate Finance Committee. Grassley’s office had developed a reputation for a willingness to conduct exacting oversight of both parties. And Foster’s team, by all accounts, found common ground with Democratic staffers.

But during those years, Foster privately expressed intensely partisan and controversial beliefs on his blog, which he maintained from 2005 to 2009. He initially took the name “extremist,” an alias he described to his readers as a tongue-in-cheek joke, then later discarded it and wrote under his first name.

While examining Foster’s record on the Hill, ProPublica discovered the blog by conducting web searches for various usernames Foster had employed online. Its contents were publicly accessible.

But after we contacted Foster for this story, the blog was set to private, requiring permission from the site’s owner to enter. (Foy, Grassley’s spokesman, initially declined to answer questions about the blog, saying the office did not have access to its contents.)

On the blog, one of Foster’s primary targets was Islam. He described Muhammad as a rapist and child abuser who had spawned “a religion that tends to lead large numbers of its followers to excuse the murder of innocents as God’s will.”

After the mayor of London spoke out against vilifying Muslim residents of the city in the wake of a foiled car bomb attack there, Foster labeled him a “Dhimmi” — a historic term that describes non-Muslims in Muslim-controlled lands.

While Foster acknowledged that most Muslims “are not terrorist sympathizers,” he referred to “the Islamic propensity for violence” and declared that “some cultures are better than others, no matter what the multicultural fetishists say.”

Jason Foster sits behind Sen. Chuck Grassley as former FBI Director James Comey testifies before the Senate Judiciary Committee on May 3, 2017, in Washington, D.C. (PBS)

Foster took a more forgiving tone with Christian extremists: “Are there a couple of isolated violent nuts who call themselves ‘Christian.’ Sure. Do you see posters and t-shirts of these people on sale throughout the Bible belt? No.”

Foster also held forth on a variety of other subjects. For instance, he dismissed criticism of the federal government’s response to Hurricane Katrina: “Some here are complaining that hurricanes don’t practice affirmative action.”

On multiple occasions, he drew parallels between same-sex marriage and incest: “What neutral principle,” he asked, “distinguishes brother-sister marriage from homosexual marriage?”

Foster called former Attorney General Eric Holder’s stance that waterboarding was torture “more than just wrong. It’s dangerous.”

He also described immigration as one of his top concerns, framing the state of play in stark terms: “I’m not willing to go so far as to say that we are under invasion,” he said, but he worried that it sure seemed like “we want to be annexed.”

In multiple posts, he questioned the patriotism of liberals, who he accused of “anti-American tendencies.”

Of Joe McCarthy, he opined that history’s condemnation of the disgraced Wisconsin politician may have been too harsh, suggesting his excesses were less of a problem than the Communist threat he was fighting.

For weeks, Foster did not respond to ProPublica’s questions about the contents of his blog. On Monday night, however, he sent a lengthy explanation. He said he thought he had taken the blog offline years ago “after people in my life helped me learn from my mistakes.”

“I regretted it then and thought I had put it behind me,” Foster said in an email. “I was mortified to learn recently that an old copy was still accessible and have since taken it down as well.”

Foster said he believed the blog was “read mostly, if at all, by a small group of friends, family, and acquaintances with a shared religious tradition and philosophical interests.” He said his writings were not meant to be taken seriously, and were not “part of my professional demeanor then or now.”

“It’s embarrassing to re-read some of the overly-provocative comments many years later with their tortured logic, dumb analogies, sarcasm, and self-righteousness,” he wrote. “Especially in the context of a vigorous discussion about controversial topics, trying to make points through excessive exaggeration was unwise and unproductive. It reminds me of why I stopped and is reinforcing the lessons I learned from the experience.”

Foster said that in certain instances, concerning harsh comments on Islam, he had been quoting others and merely wondering about the implications if such ideas were true.

“Regardless,” he wrote, “I do not excuse my poor judgment. To those hurt by what I said, I am sorry and ask for your forgiveness.”

It’s impossible to determine how large a following the blog had. Comments on the posts make it clear Foster had fans as well as detractors, some of whom challenged him on his more controversial ideas.

Stephen Kohn, executive director of the National Whistleblower Center, contacted ProPublica Tuesday to vouch for Foster’s integrity. Kohn said Foster was responsible for Grassley’s intervention on behalf of an FBI agent of Egyptian Coptic Christian descent, who accused the bureau of freezing him out of terrorism investigations after 9/11 because of his ancestry. Asked about the contents of the blog, Kohn said:

“In my dealings with him on this case, not only was there no evidence of discrimination, he was the driving force to defend him on the Hill,” Kohn said of Foster’s support for his client.

Foster had set aside the blog by the time he went to work on the Senate Judiciary Committee in 2011, when Grassley traded in his leadership role on the Finance Committee to become the top Republican on the panel.

Judiciary Committee investigators such as Foster enjoy broad authority to probe the Justice Department and its various components, such as the FBI and the Drug Enforcement Administration.

Initial leads for investigations can come from whistleblowers or news reports. Investigators have the power to demand agencies turn over documents, to subpoena witnesses who don’t cooperate or cite them for contempt. Ultimately, they chronicle their findings in public reports, refer their targets for criminal prosecution or shape legislative reforms meant to address problems they discover.

Foster was credited for his commitment to protecting whistleblowers.

Peter Forcelli, who had been a supervisor in the Phoenix field office of the Bureau of Alcohol, Tobacco, Firearms and Explosives, described being “radioactive” at work after he testified before Congress about problems with the agency’s “Fast and Furious” operation. Foster led the congressional probe into the Obama-era scandal, in which federal authorities lost track of hundreds of firearms, including two found at the scene of a shootout that killed a Border Patrol agent.

Sen. Grassley and Foster, right, at a Senate Judiciary Committee hearing about Operation Fast and Furious, on Nov. 8, 2011 (C-SPAN)

“Jason kept his word throughout the entire time. When I had problems, they were very responsive in keeping me protected,” said Forcelli, who now heads up the agency’s Miami field office.

But Foster’s investigation, done in conjunction with Rep. Darrell Issa’s staff in the House, was also marred by leaks of sensitive law enforcement information and allegations of partisan mischief directed at both Grassley and Issa. The probe seemed to generate outlandish accusations, unsubstantiated by evidence but aired publicly.

One theory was that the Obama administration had somehow purposely sabotaged the Fast and Furious program to win support for tougher gun control restrictions. Former aides recall that soon after Foster shared such suspicions privately, his boss began raising them publicly, even though the committee had found no proof of the claim.

“My suspicion is they don’t like the Second Amendment the way it is, and they want to do everything they can to hurt guns and restrict guns,” Grassley said at the time. “So they could have been building a case for that. But I can’t prove that.”

Foy, Grassley’s spokesman, denied being responsible for leaks about the Fast and Furious inquiry and defended the office’s practice of airing allegations publicly.

“When Senator Grassley seeks answers from government agencies about allegations his office receives from others, it is often misreported as the Senator accusing an agency of wrongdoing,” Foy said. “However, his letters give agencies an opportunity to respond, and making the correspondence public incentivizes them to do so.”

Following Trump’s inauguration, Grassley, as the judiciary chairman, found himself and his staff at the center of a series of explosive events.

The FBI was investigating potential links between the Kremlin and the Trump campaign.

Attorney General Jeff Sessions had been an adviser for that campaign, and recused himself from overseeing the FBI’s investigation.

Then FBI director James Comey was fired, raising questions of whether the president was attempting to obstruct the Russia probe.

Some held out hope that as complicated and fraught as the issues were, the Judiciary Committee might be able to conduct a bipartisan investigation.

But as Mueller’s team has brought charges against 19 people, including former Trump campaign officials, and the president has pushed back with claims of a “witch hunt” and made repeated attacks on the FBI, Democrats have accused Grassley’s office of helping to muddy the waters.

Danielle Brian, director of the Project on Government Oversight, a good government group that has worked closely with Grassley’s office, said she was initially optimistic because Grassley and Foster had shown a willingness to take on the White House.

When the Trump administration, for example, allowed federal agencies to essentially stop responding to requests for information from Democrats in Congress, Grassley blasted the decision and said the Justice Department’s legal rationale supporting the policy showed a “shocking lack of professionalism and objectivity.”

“That was Jason,” said Brian. “It’s deeply ingrained in Grassley and his team: They are institutionalists, they remember being in the minority. They care about the institution of Congress.”

But Brian and others have been baffled by what has happened in the months since – by the open hostility between the committee’s two sides, the unusual criminal referral, the seemingly disproportionate scrutiny Grassley and Foster have been applying to those involved in the investigation of Trump and his team.

“It’s impossible for me to reconcile,” she said. “It doesn’t make sense.”

In addition to questioning Comey’s handling of classified material and calling for another investigation of matters related to Hillary Clinton, Grassley’s office took aim at Fusion GPS, the firm that commissioned what became known as the Trump-Russia dossier. Grassley asked whether the firm had violated the law by not registering as a foreign agent for work it did on another case. Grassley and Foster also brought Glenn Simpson, the firm’s co-founder, in for a confidential interview.

In that August interview with Foster and other judiciary staffers, Simpson confirmed the identity of his company’s bank. The information was sensitive because the firm’s bank records, if successfully subpoenaed, could reveal clients who are promised confidentiality.

In October, the House Intelligence Committee subpoenaed the bank for Fusion’s records.

Fusion fought the requests in court, suggesting to the judge that someone on Grassley’s committee provided information to the House committee “in order to circumvent the rules.” The Senate panel cannot issue subpoenas without bipartisan support, but the House committee can.

One of the people in court to watch the proceedings was Foster.

Grassley’s spokesman said they became aware of the bank name from a confidential source before the Simpson interview, and that no one from the senator’s staff leaked the name. Asked about Foster’s presence in court, the spokesman said “these proceedings are relevant to our work.”

Another incendiary matter involved the public disclosure of the names of Fusion GPS employees, something the firm complained might endanger them. Grassley’s office blamed Fusion for the disclosure, and downplayed the risk to the employees since the firm had not provided the committee with “specific threat information.”

Democratic frustration with Grassley boiled over when he and Sen. Lindsey Graham, R-S.C., produced the public criminal referral against Steele.

A former Republican congressional aide said it was particularly puzzling that the referral was made publicly because if charges were filed, it may have appeared as though the DOJ caved to political pressure.

A current Republican aide familiar with Judiciary Committee operations told The Washington Post: “It’s pretty clear that Grassley and Graham are interested in carrying water for the White House, but that is not reflective of the whole committee.”

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The criminal referral appeared to be the last straw for the committee’s top Democrat. Sen. Dianne Feinstein of California, who said she wasn’t consulted beforehand and called it “another effort to deflect attention.” A few days later, she released the committee’s confidential Fusion interview transcript, a move she made without Grassley’s permission and that further inflamed partisan distrust on the committee.

Feinstein said the disclosure would dispel the “innuendo and misinformation” being circulated by Republicans seeking to deflect attention from the committee’s look at Trump and his campaign.

Several current and former legislative aides noted that, in an earlier statement, Feinstein seemed to indicate it wasn’t Grassley who she considered primarily responsible for the growing divide.

She blamed “staff” for trying to shift the focus of the committee’s work to Hillary Clinton and the Obama administration.

In a lengthy series of written responses to ProPublica’s questions, Foy, Grassley’s spokesman, denied that Foster or the chairman’s other staffers had placed the interests of the president over an independent investigation. The Democrats, Foy said, were the ones playing politics.

“Ranking Member Feinstein has personally told Chairman Grassley on multiple occasions that she is unwilling to look into Clinton-related matters, and has staunchly resisted oversight efforts relating to Fusion, Steele, the dossier, and the FBI,” Foy wrote. “Refusing to look at issues on your own side of the aisle seems like the definition of partisanship. Accusing the other side of playing defense for the White House while your side plays defense for the DNC and the Clinton campaign looks like the very definition of partisanship.”

Foy said there were attempts by Grassley’s office “to be good faith partners to work together to ask hard questions of both sides.” Grassley, Foy said, had supported information requests related to the Trump camp, helping to secure thousands of pages of documents from the Trump campaign, companies and presidential transition. Grassley’s office also pointed to its work to get interviews with Donald Trump Jr., along with others present at the now infamous 2016 Trump Tower meeting involving Trump’s family members, campaign officials and Russians allegedly looking to provide dirt on Hillary Clinton.

Grassley’s office provided ProPublica with a private letter from Grassley to Feinstein, in which he criticizes Feinstein for requesting the committee withdraw its subpoena requiring Trump campaign chairman Paul Manafort’s testimony at a public hearing last year, because she was unsatisfied with the limited scope of questions he would answer. Since Manafort has now been indicted, his attorney has indicated he would refuse to answer any questions. In the letter, Grassley blames Feinstein for not being “willing to move more quickly and take ‘yes’ for an answer.”

The failure to interview Manafort is considered one of the committee’s most significant errors.

“The Chairman was then criticized for letting him off the hook,” Foy said. “In reality, the Ranking Member requested that the Chairman dismiss Manafort from the subpoena. He acquiesced to her request, even though it was the Chairman’s preference to require him to appear.”

Feinstein would not be interviewed for this article, and her spokesman would not comment on Foster, his role on the committee or his blog. The office repeated Feinstein’s insistence that the committee’s mandate was to investigate Russian interference in an American election, and the president’s possible role in obstructing the criminal inquiry into the nature of that interference.

“As a rule, Judiciary Committee Democrats have made their investigative decisions based on an objective review of facts,” said Tom Mentzer, a spokesman for Feinstein.

Kris Kolesnik, a former top adviser to Grassley, was asked years ago to help train young aides arriving on Capitol Hill on how to conduct fair investigations. In a recent column about the experience, Kolesnik recounted the advice he gave.

“Construct a wall between campaigning and governing. In a campaign, you can knock yourself out playing politics. But once you’re in government, you can only go as far in successful oversight as your credibility takes you,” Kolesnik wrote.

The column went on to lament how battered that notion has become. Kolesnik blamed his own party, accusing Republicans of standing in the way of the truth for political gain.

He wrote he knew “a congressional player in the Russia probe is having discussions with the White House about a possible job.”

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According to Foy, Grassley’s spokesman, Foster was “encouraged by others” last year to consider an inspector general position in the Trump administration. After he interviewed with the independent body that vets candidates, Foster learned the panel recommended him to the White House Counsel’s office. Foster solicited advice about continuing the process, but declined to pursue it further in September. Then, in November, he was again encouraged to consider an inspector general post, mulled it over, but ultimately declined in December.

Foy would not say who specifically encouraged Foster to consider such an appointment, or whether he discussed the job with a White House official, saying any such preliminary conversations with the White House were routinely kept confidential. (A person who spoke to Foster told ProPublica Foster had indeed talked to a White House official during his deliberations.)

Foy said Foster notified Grassley of the job possibility, and pledged to recuse himself from White House matters if he consented to go through the full White House vetting process, rather than waiting until a formal offer had been made, as required by Senate ethics rules.

Still, during the period that Foster was considering an executive branch appointment, the committee’s inquiries relating to the Russia investigations were in full swing and Democrats were growing increasingly frustrated with what they perceived as stalling by Grassley’s office.

Grassley’s spokesman said there is nothing unusual about an administration soliciting congressional staffers from their own party for positions, and that “such preliminary discussions do not trigger an obligation to recuse from White House related matters.”

Congressional experts from left- and right-leaning organizations countered that taking part in a sensitive investigation relating to a sitting president while under consideration for a job in that president’s administration creates the appearance of a conflict even if it’s not a violation of ethics rules. Foster’s deliberations about a job with the administration, they said, should have been disclosed to ethics officials and the rest of the committee, and likely required his recusal.

“Frankly on its face, this is unethical behavior,” said Norman Ornstein, who helped create the House’s ethics watchdog agency and is now a scholar at the conservative American Enterprise Institute.

Experts were also concerned that Foster was being considered for an inspector general role considering the beliefs he expressed on his blog.

Stephen Street, president of the Association of Inspectors General, speaking generally, said bigoted views should be disqualifying.

“When you talk about racism, that obviously can’t be tolerated,” he said. “You don’t want to have a situation where people don’t trust your work product because of views you may have expressed that show bias.”