WASHINGTON -- Sen. Susan Collins, R-Maine, said Sunday on "Face the Nation" that important elements of President Donald Trump's interactions with former FBI Director James Comey are the tone and "exact words" that were spoken.

Collins was discussing Comey's scheduled testimony -- set for Thursday -- before the Senate Intelligence Committee. He is expected to discuss his interactions with Mr. Trump, and reports that -- according to a memo Comey wrote -- President Trump asked him to drop an investigation into former National Security Adviser Michael Flynn.

"It's so important for us to hear from Mr. Comey before our committee, as well as other witnesses," said Collins, who is a member of the committee. "The acting director of the FBI also said that there'd not been an attempt to influence the investigation. And yet, we hear of all these memos to the file, all of these dinners and meetings between President Trump and the F.B.I.-- the former F.B.I. director. So we need to hear directly from Mr. Comey on these important issues."

Collins says that while the investigation into Russian meddling in the 2016 election is "taking up a great deal of time" the committee is eager to question Comey on the circumstances following his recent termination.

"There's a very interesting phrase in which he says, 'While I am very grateful that you, on three separate occasions, informed me that I was not a subject of the investigation...,'" Collins said. "That phrase raises a lot of questions in my mind. Does Mr. Comey agree that that is what was said? Why would he tell the President that? What was the tone and the context of those discussions on three different occasions, if they in fact are accurately portrayed in this letter?"

When pressed on the magnitude of the Russia investigation as the committee enters an important week of hearings, Collins said "there is so much speculation and so many stories and so many leaks that it's very difficult to determine the facts of the Russian involvement in our elections last fall, the extent to that of that involvement, and also whether or not there was collusion or collaboration with members of President Trump's campaign team."

Collins added that while the committee would still benefit from having an "experienced special investigator" to oversee the ongoing investigations, she commended the staff of experts and the intelligence community for the extraordinarily complex work being done thus far.

"I will say, every member of the committee has been extremely active in reviewing the evidence that we do have so far."