Once a special assistant to former FBI Director James Comey, Josh Campbell was present when Comey first briefed a newly-elected President Donald Trump, telling the soon-to-be leader about reports circulating that he had been compromised by the Russians.

As the rest of America now knows, that was the beginning of the end for Comey’s career, and set up a tension between Trump and American intelligence agencies that has persisted throughout his presidency.

That tension is the subject of Campbell's new book, “Crossfire Hurricane: Inside Donald Trump's War On The FBI." Campbell is now also a CNN law enforcement analyst.

Campbell told host Adam Reilly, in for Jim Braude, on Greater Boston that Trump's repeated attacks on the FBI have weakened the agency.

“During the course of the Russia investigation, we had a president who was constantly attacking and undermining the credibility of the institution,” he said.

He said the FBI should certainly not be immune from all criticism — its handling of the prosecution of Whitey Bulger a particularly salient local example. But Campbell believes Trump’s attempt to erode American confidence in the FBI is dangerous.

“If the American people believe this narrative that the FBI is corrupt ... that’s going to make us less safe,” Campbell said.

“This whole idea that the FBI was targeting the president or a campaign for partisan reasons is simply nonsense,” he added.