The memo in question documents the three day debriefing of Christopher Steele's supposed "subsource." The relevant portion of the interview can be found between the 9:50 and 11:15 minute marks. Here is my transcription of that portion:
... I believe that the FBI was on notice that it [the Steele dossier] was unreliable, continued to use it anyway. I believe that they misled the FISA court, and here's the key question.
On January 21st through the 24th the Russian subsource, the guy who provided ALL the material for the dossier, is interviewed by the FBI for three days. He's interviewed again in March. There's a memo about that interview. Horowitz found it. It was 40 pages. My staff has finally got to look at it--it's classified. I'm gonna try to get it UNclassified. The Horowitz Report suggests that the result of the Russian subsource interview put great doubt into the reliability of the dossier in terms of being able to get a warrant.
Here's the question. Is it possible that an interview of that magnitude--that basically shredded the key document to get a warrant--that the people at the top, McCabe and Comey, were never told, 'Oh, by the way, our entire case has collapsed.' I'm looking at that.
I believe I can answer that question: No. That's not possible.
Chuck Ross at the Daily Caller comments:
The Justice Department’s office of the inspector general revealed in a report released Dec. 9 that the source, who has not been identified, disputed many of Steele’s allegations of collusion between the Trump campaign and Russia.
The source told the FBI that Steele misrepresented or embellished the claims by passing off rumor as fact in the 35 page dossier. The inspector general’s report revealed that the FBI failed to disclose the information in two applications for Foreign Intelligence Surveillance Act (FISA) orders against Carter Page, a former Trump campaign aide.
The FBI relied heavily on Steele’s information in applications for the FISAs. The Justice Department deemed two of the four FISA orders against Page to be invalid because of omissions about Steele’s source.
If Graham is stating openly that he's seeking to declassify this memo, I assume he's coordinating those efforts with the Trump administration's ultimate Declassification authority: AG Bill Barr. The existence of this memo is not news to Barr, Durham, or Graham, so the suspicion must be that Barr has decided that the time for declassification is near.