Story highlights Comey, the source said, believed Trump did not quite grasp the inappropriateness of his actions

Comey is scheduled to testify before the Senate intelligence committee on Thursday

Washington (CNN) Former FBI Director James Comey was "disturbed" by his interactions with President Donald Trump but "he thought he had the situation under control," a source familiar with Comey's thinking tells CNN.

Comey, the source said, believed he was dealing with someone who did not quite grasp the inappropriateness of his actions, and that Comey thought the President could be "trained" how to interact with the FBI director. Comey considered it, the source added, as "an ongoing policing project."

Comey, fired by Trump last month, is scheduled to testify before the Senate intelligence committee on Thursday.

It is reasonable to conclude, the source added, that Comey did not think any of Trump's individual actions constituted obstruction of justice. But, the source said, there is a question of whether the "aggregate pattern of behavior" could be seen very differently, especially after the President fired Comey.

JUST WATCHED Gergen: Invoking executive privilege a mistake Replay More Videos ... MUST WATCH Gergen: Invoking executive privilege a mistake 01:06

Trump later told NBC News that he had considered "this Russia thing" when he let Comey go.

Read More