Comey's interactions with Trump have come under intense scrutiny since his firing last month, causing some lawmakers to question whether it was related to the ongoing FBI investigation into alleged Russian meddling during the 2016 presidential election.
Among the Senate Intelligence Committee's primary inquiry will be to ask Comey about those encounters and the contemporaneous notes he reportedly took of his meetings with the president.
At the meeting where Comey is said to have rebuffed the president's reported loyalty pledge, one source described Comey as viewing the attempt as an amateurish effort to bring him under the president's wing.
During their meetings, Comey was constantly assessing the president's motive, unsure whether Trump was doing something sinister or was someone simply used to getting his way and not versed in the protocols of Washington whereby the FBI director enjoys broad independence.
For its part, the White House has previously disputed published media accounts of the Comey and Trump meetings.
But Comey was concerned enough to make sure he was taking notes about certain meetings, especially the one in which Trump suggested he go easy on Flynn. Comey made no final conclusion about the encounter but decided to chronicle it for the future.
Comey wanted to simply continue the investigation and keep the president at arm's length –- not doing anything that would taint investigators' view of the president, but maintaining notes that would be there in case something dramatic happened later on.
ABC's sources say that Comey will not volunteer a belief that Trump committed obstruction of justice in his interactions with the former FBI director, as Comey believes that judgment is the purview of investigators and special counsel Mueller.
Rather, Comey is said to view himself merely as a witness who will answer questions about the president in a straightforward manner.
Comey is suspicious, and some sources close to him are not exactly certain how Comey would respond to questions about how Trump's actions toward him now look in hindsight, knowing everything that has transpired since his firing.