Former FBI Director James Comey is busy writing opinion columns and appearing on cable news town halls about the Mueller report, but a former top official at the bureau says Comey has three very good reasons to be worried as the Department of Justice examines how the Trump-Russia probe started in the first place.

Kevin Brock served 24 years in the FBI, including a stint as deputy director for intelligence.  He was also principal deputy director at the National Counterterrorism Center.  Brock is now head of NewStreet Global Solutions.  He says Comey's first problem is providing evidence that an investigation was warranted in the first place and Mueller's report makes the case harder to make.

"If there no findings of any type of collusion as they say between the Russians and the Trump campaign, what was the FBI going on in the first place to initiate the case?" asked Brock.

During last week's Senate testimony, Attorney General William Barr also wondered aloud why the FBI didn't just contact the Trump campaign about any figures feared to be conspiring with Russia - or the suspicious campaign officials themselves.

Brock says launching a surveillance effort on American citizens without first going to them is highly unusual.  According to Brock, under a preliminary investigation, the standard protocol is to warn Americans about who their foreign contacts really are and to encourage cooperation with the FBI.

And he says there are specific things you cannot do during a "PI."

"You may not cast existing sources or start new sources and target that U.S. person.  You may not appeal to the FISA court to get a warrant to intercept the communications  of that person.  You may not pull their financial records.  It's very limited in scope," said Brock.

Brock says probing the the basis for a FISA warrant will also put the heat on Comey.

"Electronic surveillance of a U.S person is an incredibly invasive, investigative technique.  I've referred to it as the nuclear option of intelligence collection.  There is nothing that is more invasive of privacy than a FISA court-ordered warrant to monitor all of your communications," said Brock.

Former FBI Deputy Director Andrew McCabe testified to Congress that the Steele dossier was a major component of the request for a FISA warrant.  Brock says that premise was very flimsy.

"They relied heavily on this dossier that is clearly a political document.  It should not have been the foundation of any warrant for intercepting an American citizen.  That appears to be clear," said Brock.

Listen to the full podcast as Brock also explains the evidence suggesting Comey knew full well he was part of a political operation rather than one focused on criminal justice and what he expects to learn in the forthcoming report from Justice Department Inspector General Michael Horowitz.