There's a huge hole in Barr's summary of the Mueller report -- according to top counterintelligence experts

Attorney General William Barr's summary of the special counsel report overlooks one of key aspects of the investigation into President Donald Trump's ties to Russia.

The FBI opened a counterintelligence investigation shortly after Trump fired the bureau's director James Comey, although it's not clear what happened to that probe after Robert Mueller was appointed special counsel, reported The Atlantic.

“We were concerned, and we felt like we had credible, articulable facts to indicate that a threat to national security may exist,” said former FBI Deputy Director Andrew McCabe.

That counterintelligence investigation was aimed at determining whether the president was acting as a Russian agent -- which presents an immense challenge.

“Normally, the bureau would investigate," said Jeremy Bash, former chief of staff at the Defense Department and the CIA during the Obama administration, "and if criminal matters were involved, they’d ask prosecutors to get involved. 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.”

Trump sought real estate ventures in Moscow during the 2016 campaign, which he and his lawyer Michael Cohen lied about, but that still doesn't fully explain his odd devotion to Russian president Vladimir Putin.

“We still do not understand why President Trump has this affinity for Putin," said former CIA Deputy Director Michael Morell. "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.”

Barr's summary showed Mueller apparently determined there was not enough evidence to prove a criminal conspiracy case, but that's a different standard of proof than what a counterintelligence investigation would determine.

“(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,” said JOhn McLaughlin, the former acting CIA director under former Presidents Bill Clinton and George W. Bush.

That distinction is crucial to understanding what evidence Mueller was looking for, and it's something that Barr ignored in his summary.

“If all we do is provide criminal standards to investigative findings, we are missing the point,” said Frank Figliuzzi, the former assistant director for counterintelligence at the FBI.

Most counterintelligence cases don't result in criminal prosecution, but are intended to determine whether a foreign power targeted, compromised or recruited the subject of the investigation.

“This thing started as a counterintelligence investigation,” Figliuzzi said, “and it needs to end as a counterintelligence investigation.”