Late last summer, the director of the Federal Bureau of Investigation, James Comey, met with John Giacalone, the bureau official responsible for everything from counterterrorism to counterintelligence across the U.S. Giacalone, a fireplug of a man who started out as a New York City field agent battling organized crime in the 1990s, wanted to brief Comey on a high-profile issue that had been referred to the bureau by the Inspector General of the Intelligence Community. Emails found on the private, unclassified server used by Hillary Clinton as Secretary of State contained classified information; Giacalone’s National Security Branch wanted to investigate how the secrets got there and whether anyone had committed a crime in the process. Comey was clear about one thing. “He wanted to make sure it was treated the same way as all other cases,” says Giacalone, who left the bureau in February.

For more on James Comey and the FBI’s investigation into Hillary Clinton’s e-mails, read the April 11, 2016, issue of TIME.

Seven months later, 20 to 30 agents, technical specialists and analysts have been assigned to the investigation, according to sources familiar with it. The agents have conducted interviews and done forensic analysis of the evidence collected. And they have executed process, the sources say, referring to a category of investigative tools that can include, among other things, subpoenas. As they near the end of the investigation, the agents are preparing to interview several of Clinton’s closest aides, and perhaps the candidate herself, according to the sources, a move Clinton campaign officials say she will comply with. Attorney General Loretta Lynch told Congress on Feb. 24 that she is awaiting a recommendation from Comey and the FBI on whether anyone should be charged.

Comey is keeping a close watch on the investigation, getting briefings from team leaders and personally overseeing the case. Agents have been told they may be polygraphed to prevent leaks, the sources familiar with the probe say. “I want to ensure [the Clinton email investigation] is done in the ways the FBI does all its work: professionally, with integrity, promptly,” Comey told Congress in February. “And without any interference whatsoever.”

Some Republicans are referring to his recommendation as the “Comey primary” in the hopes it will sway the election their way. That may be wishful thinking, but one thing is clear: Comey has spent much of his career investigating and occasionally confronting high-profile public figures, including the Clintons.

Comey’s first brush with them came when Bill Clinton was president. Looking to get back into government after a stint in private practice, Comey signed on as deputy special counsel to the Senate Whitewater Committee. In 1996, after months of work, Comey came to some damning conclusions: Hillary Clinton was personally involved in mishandling documents and had ordered others to block investigators as they pursued their case. Worse, her behavior fit into a pattern of concealment: she and her husband had tried to hide their roles in two other matters under investigation by law enforcement. Taken together, the interference by White House officials, which included destruction of documents, amounted to “far more than just aggressive lawyering or political naiveté,” Comey and his fellow investigators concluded. It constituted “a highly improper pattern of deliberate misconduct.”

Comey parlayed the Whitewater job into top posts in Virginia and New York, returning to Manhattan in 2002 to be the top federal prosecutor there. One of his first cases as a line attorney in the same office 15 years earlier had been the successful prosecution of Marc Rich, a wealthy international financier, for tax evasion. But on his last day as President in 2001, Bill Clinton pardoned Rich. “I was stunned,” Comey later told Congress. As top U.S. prosecutor in New York in 2002, appointed by George W. Bush, Comey inherited the criminal probe into the Rich pardon and 175 others Clinton had made at the 11th hour.

Despite evidence that several pardon recipients, including Rich, had connections to donations to Bill Clinton’s presidential library and Hillary Clinton’s 2000 Senate campaign, Comey found no criminal wrongdoing. He was careful not to let the investigation be used for political purposes by either party. When pressed for details in one case, he said, “I can’t really go into it because it was an investigation that didn’t result in charges. That may be a frustrating answer, but that’s the one I’m compelled to give.”

Comey hasn’t only discomfited Democrats. As Bush’s Deputy Attorney General Comey launched the probe into the leak of the identity of CIA officer Valerie Plame and briefly blocked the National Security Agency’s Stellar Wind program of blanket telephone-metadata after a dramatic confrontation with then-White House Counsel Alberto Gonzales. Comey’s stand against Gonzales didn’t end there, and its fallout has implications for the current Clinton email investigation. In May 2007, Comey had left government, and Gonzales, who had replaced John Ashcroft atop the Justice Department, was clinging to his job amid unrelated scandals. Comey surprised the top Democratic staffer on the Senate Judiciary Committee by agreeing to make public the details of the Stellar Wind confrontation for the first time in compelling open testimony. The hearing was designed to force Gonzales out, and ultimately it worked. Comey’s testimony led to the discovery by White House lawyers that Gonzales had improperly stored classified notes on Stellar Wind, which in turn led to his resignation that August, according to top Bush White House officials. Comey and Gonzales both declined to comment on the matter.

Lawyers preparing Clinton and her aides for possible interviews are well aware that Comey has a history of prosecuting those who impede investigators. Cheney’s aide Libby was convicted not of leaking Plame’s identity but of obstructing justice, as was Martha Stewart. Comey had a front-row seat to Clinton’s controversial handling of documents in the White-water case. Ultimately the Senate committee he worked for two decades ago found no criminal wrongdoing but issued a politically damaging report anyway. Clinton campaign official Brian Fallon says that the FBI has not requested an interview with her yet and that she remains ready to cooperate with the probe. “She first expressed her willingness to cooperate in any way possible last August,” says Fallon, “and that included offering to meet with them and answer any questions they might have.”

Comey’s recommendation to Lynch, when it comes, could include a description of the evidence; what laws, if any, might have been violated; and how confident he is in the results of the probe, the sources familiar with the investigation tell TIME. What will come of the Comey primary? Says Giacalone: “If the evidence is there, it’s there. If it leads to something inconclusive, or nothing, he’s not going to recommend filing charges.”

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