While his House colleagues spent the day trying to get Mueller to say that the president should be impeached—or, alternatively, from the GOP’s perspective, that investigation was corrupted from the outset—it was left to Krishnamoorthi, a lawyer who represents a district in the suburbs of Chicago, to pick up the thread of Mueller’s largely-forgotten counterintelligence investigation. Mueller was tasked with conducting that investigation when he was appointed as special counsel in May 2017.

As Mueller’s report later revealed, it was then–FBI director James Comey’s testimony about the counterintelligence investigation to the House Intelligence Committee that so infuriated the president and set in motion the events that led to Comey’s firing and then, Mueller’s appointment. Under the special counsel, the counterintelligence investigation quickly shifted gears to a criminal investigation, but the original probe that Mueller inherited never went away. While the public’s attention was focused on the multiple convictions, guilty pleas, and charges against 34 individuals and three companies, the counterintelligence investigation continued quietly running below the surface. And, as Mueller’s Wednesday testimony suggests, it still continues.

The fruits of this inquiry may never be seen in public because its primary mission isn’t to investigate and prosecute crimes. The job of FBI counterintelligence was and is to neutralize the threat posed by foreign intelligence—which, in this case, means dealing with what the special counsel’s report called Russia’s “sweeping and systematic” effort to interfere in the 2016 presidential election. But the investigation’s low visibility shouldn’t diminish its importance, which is no less than a probe into whether the president himself was acting on behalf of Russia’s interests.

The FBI, as the lead agency for exposing, preventing, and investigating intelligence activities on U.S. soil, sent officials with the bureau’s Counterintelligence Division to meet regularly with members of the special counsel’s team. For more than a year, FBI agents were embedded in Mueller’s office. Their purpose, according to a little-noticed section of the special counsel’s report, was “to review the results of the investigation and to send—in writing—summaries of foreign intelligence and counterintelligence information to FBIHQ and FBI Field Offices.” But not all of the information in those summaries appeared in Mueller’s final report.