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(CNN) —  

In the hectic eight days after President Donald Trump fired FBI Director James Comey, Deputy Attorney General Rod Rosenstein and top FBI officials viewed Trump as a leader who needed to be reined in, according to two sources describing the sentiment at the time.

They discussed a range of options, including the idea of Rosenstein wearing a wire while speaking with Trump, which Rosenstein later denied. Ultimately, then-acting FBI Director Andrew McCabe took the extraordinary step of opening an obstruction of justice investigation even before special counsel Robert Mueller was appointed, the sources said. The obstruction probe was an idea the FBI had previously considered, but it didn’t start until after Comey was fired. The justification went beyond Trump’s firing of Comey, according to the sources, and also included the President’s conversation with Comey in the Oval Office asking him to drop the investigation into his former national security adviser Michael Flynn.

The new details about the genesis of the obstruction case into Trump that became a key element of the Mueller probe shed light on the chaotic week following Comey’s firing and the scramble to decide how best to respond. They also help to explain the origins of the Mueller investigation that has stretched across 19 months, consumed Trump’s presidency and is building toward a dramatic day of courtroom filings on Friday.

A Justice Department official strongly disputed Rosenstein sought to curb the President, emphasizing that his conversations with McCabe were simply about talking through ways to conduct the investigation. “He never said anything like that,” the source added.

Other sources said that the FBI would only take such dramatic action if officials suspected a crime had been committed. But Rosenstein and other senior FBI officials also had deep concerns about Trump’s behavior and thought he needed to be checked, according to the sources.

A spokeswoman for McCabe did not provide comment for this story.

“It’s shocking that the FBI would open up an obstruction case for the President exercising his authority under Article II,” said the President’s attorney Rudy Giuliani.

The Washington Post first reported last year that the obstruction investigation started before Mueller’s appointment, but the sources offered a more complete picture of the drastic actions law enforcement leaders took during that feverish period.

Prior to Comey’s firing, top FBI officials had discussed opening an obstruction investigation based on the President saying to Comey, “I hope you can let this go” when discussing Flynn. That episode was later described in memos Comey wrote following the February meeting that the former FBI director would leak soon after his firing.

Comey’s attorney did not comment for this story, but pointed to Comey’s 2017 testimony to the Senate Intelligence Committee.

Comey, however, hinted at the discussion in his book.