On Sunday afternoon, Attorney General Bill Barr presented a summary of Special Counsel Robert Mueller’s conclusions that contained a few partial sentences from Mueller’s final report, one of which directly addressed the question of collusion between Donald Trump’s campaign and Russia: “The investigation did not establish that members of the Trump campaign conspired or coordinated with the Russian government in its election interference activities.” In a footnote, Barr explained that Mueller had defined “coordination” as an “agreement—tacit or express—between the Trump campaign and the Russian government on election interference.”

Mueller’s full report has not been made available to the public yet, so it’s not clear whether it sets forth everything the special counsel’s office learned over the course of its nearly two-year investigation—including findings about conduct that was perhaps objectionable but not criminal—or whether it is more tailored and explains only Mueller’s prosecution and declination decisions. But national-security and intelligence experts tell me that Mueller’s decision not to charge Trump or his campaign team with a conspiracy is far from dispositive, and that the underlying evidence the special counsel amassed over two years could prove as useful as a conspiracy charge to understanding the full scope of Russia’s election interference in 2016.

Read: What Mueller leaves behind

“As described by Barr, at least, Mueller’s report was very focused on criminal-law standards and processes,” said David Kris, a founder of Culper Partners, who served as the assistant attorney general for the Justice Department’s National Security Division under former President Barack Obama. “We won’t know for sure if that is the case, and if it is the case, why Mueller confined himself in that way, until we see the full report.” Kris noted, however, that “there is no question that a counterintelligence investigation would have a wider aperture than a strict criminal inquiry as applied here, and would be concerned, for example, with the motivations and any sub-criminal misconduct of the principal actors.”

A counterintelligence probe, he added, would ask more than whether the evidence collected is sufficient to obtain a criminal conviction—it could provide necessary information to the public about why the president is making certain policy decisions. “The American people rightly should expect more from their public servants than merely avoiding criminal liability,” Kris said.

A spokesman for the House Intelligence Committee said in a statement on Monday that in light of Barr’s memo “and our need to understand Special Counsel Mueller’s areas of inquiry and evidence his office uncovered, we are working in parallel with other Committees to bring in senior officials from the DOJ, FBI and SCO to ensure that our Committee is fully and currently informed about the SCO’s investigation, including all counterintelligence information.”

Read: The House’s latest move could be a big threat to Trump’s presidency

In May 2017, just after Trump fired former FBI Director James Comey, the FBI launched a full counterintelligence investigation into the president to determine whether he was acting as a Russian agent. “We were concerned, and we felt like we had credible, articulable facts to indicate that a threat to national security may exist,” former FBI Deputy Director Andrew McCabe explained to me last month. It’s still not clear what became of that counterintelligence probe after Mueller was appointed, and Barr did not indicate in his four-page summary how far the special counsel pursued it.

Read: Andrew McCabe couldn’t believe the things Trump said about Putin

Jeremy Bash, who served as chief of staff at the Defense Department and the CIA under Obama, said he believes Mueller’s “core focus” was to determine whether or not federal criminal laws were violated. “If Mueller interpreted his mandate as a criminal one, the decision to pursue the investigation as such is something he will have to explain to Congress,” Bash said.

Mueller’s mandate, given to him by Deputy Attorney General Rod Rosenstein, empowered him to investigate not only any “coordination” between the campaign and Russia, but any “links” between them as well. Barr’s summary does not describe how Mueller investigated or came to explain the many interactions the campaign had with various Russians during the election.

Even so, Bash said, it’s an “immense challenge” to envision how a counterintelligence investigation targeting the president himself would have played out. “Normally, the bureau would investigate, and if criminal matters were involved, they’d ask prosecutors to get involved,” he said. “But if it is just a matter of there being a national-security threat, the FBI would report to the director of national intelligence, who would then report to the president. But what if the president is the threat? We don’t have a playbook for this.”

Generally speaking, the wide aperture afforded by a counterintelligence investigation might be key to understanding some of the biggest lingering mysteries of the Trump campaign’s contacts with Russians in 2016—mysteries that, if solved, could explain the president’s continued deference toward Russian President Vladimir Putin and skepticism about his conduct on the part of the U.S. intelligence community.

For example, was the fact that Trump pursued a multimillion-dollar real-estate deal in Moscow during the election—and failed to disclose the deal to the public—enough for the Russians to compromise him? Why did the administration attempt to lift the sanctions on Russia early on in Trump’s tenure, even after it had been revealed that Russia had attacked the 2016 election? And what about the internal campaign polling data that Trump’s campaign chairman, Paul Manafort, gave to the suspected Russian agent Konstantin Kilimnik in August 2016—an episode that, according to one of the top prosecutors on Mueller’s team, went “very much to the heart of what the special counsel’s office is investigating”?

Mueller apparently determined that none of that evidence was enough to establish that a criminal conspiracy had occurred, which is fairly unsurprising if you know Bob Mueller, said John McLaughlin, the former acting director of the CIA who served under former Presidents Bill Clinton and George W. Bush. In criminal law, a conspiracy is an agreement between two or more persons to commit a crime.

Mueller “always noted that the term evidence meant something different to intelligence analysts who had to work with a variety of sources of varying reliability, whereas an FBI officer needed something so unassailable as to work in a court prosecution,” McLaughlin told me, referring to the conversations he had with Mueller while he was FBI director. But as former CIA Deputy Director Michael Morell, who now hosts the Intelligence Matters podcast, told me, “We still do not understand why President Trump has this affinity for Putin. What happened yesterday is Mueller took one possibility off the table—that there was a criminal conspiracy. But we still don’t know what is going on between these two leaders, and what is driving this relationship.”

It would once have been unthinkable to even contemplate that a sitting president was putting the interests of a hostile foreign power above those of the United States. But Trump’s consistent praise of Putin, his pursuit of a massive real-estate deal in Moscow while Russia was waging a hacking and disinformation campaign against the United States in 2016, and the secrecy that continues to surround his conversations with his Russian counterpart have given some in the national-security community, including many leading Democrats, pause.

Trump took the extraordinary step of confiscating his interpreter’s notes after his first private meeting with Putin in Hamburg, Germany, in 2017, according to The Washington Post, and demanded that the interpreter refrain from discussing the meeting with members of his own administration. In Helsinki, Finland, one year later, Trump insisted on meeting with Putin with no American advisers or aides present.

Frank Figliuzzi, a former assistant director for counterintelligence at the FBI, said he “never envisioned” that Mueller would bring a conspiracy charge—and that focusing on the absence of criminal indictments for conspiracy is unproductive. “If all we do is apply criminal standards to investigative findings, we are missing the point,” Figliuzzi told me. He noted that the vast majority of counterintelligence cases never result in criminal prosecution. Instead, he said, “they’re about determining the degree to which a foreign power has targeted, compromised, or recruited” the subject. “This thing started as a counterintelligence investigation,” Figliuzzi said, “and it needs to end as a counterintelligence investigation.”