"I wanted to make sure that our case was on solid ground and if somebody came in behind me and closed it and tried to walk away from it, they would not be able to do that without creating a record of why they made that decision," McCabe told Scott Pelley on "CBS This Morning" in an interview that aired Thursday.
In December, CNN reported that following the firing of FBI Director James Comey, McCabe took the extraordinary step of opening an obstruction of justice investigation into Trump before special counsel Robert Mueller was appointed in May 2017.
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McCabe told Pelley that the day after Comey's firing, "I met with the team investigating the Russia cases and I asked the team to go back and conduct an assessment to determine where are we with these efforts and what steps do we need to take going forward."
"I was very concerned that I was able to put the Russia case on absolutely solid ground in an indelible fashion that, were I removed quickly or reassigned or fired, that the case could not be closed or vanish in the night without a trace," McCabe said.
At the same time the FBI opened a probe into Trump for possible obstruction of justice following the Comey firing, counterintelligence agents were investigating why Trump was acting in ways that seemed to benefit Russia, CNN reported last month.
McCabe was fired by then-Attorney General Jeff Sessions in March following an inspector general report that concluded he misled investigators about his role in directing other officials at the FBI to speak to The Wall Street Journal about his involvement in a public corruption investigation into the Clinton Foundation.
Trump heralded McCabe's firing, calling it a "great day for the hard working men and women of the FBI - A great day for Democracy."