The Washington Post was first to report on the lengthy phone call, which occurred before Trump's stunning, hourlong phone conversation with Raffensperger in which the president ranted about baseless allegations of election fraud and pressured Georgia's top elections official to "find" enough votes to deliver him a win in the Peach State.
That call, which took place on Jan. 2, is cited in the draft article of impeachment against the president that Democrats could introduce as early as Monday.
Deputy Secretary of State Jordan Fuchs confirmed the call between Trump and the chief investigator took place without offering details, saying only: "The secretary and the secretary of state's office can confirm that the call did happen."
The White House declined to comment.
The source familiar with the matter, who requested anonymity because of the sensitivity of the call, told ABC News that the president's call to the chief investigator occurred the day after White House Chief of Staff Mark Meadows traveled to Cobb County, Georgia, attempting to observe the signature match audit taking place there. The source asked that the chief investigator remain unnamed because of the current threat environment election officials are facing.
Meadows was in the county on Dec. 22, ABC News previously reported. Fuchs said at the time that she did not allow Meadows to enter the room where investigators from Raffensperger's office and the Georgia Bureau of Investigation were doing the audit, but she did allow him to stand in the doorway.
Fuchs said that the president's chief of staff asked her "basic questions about the process," and wanted to know if they were doing a statewide signature audit. Raffensperger had previously announced his office has partnered with the University of Georgia to conduct a statewide signature audit study, which Fuchs said she told Meadows.
According to Fuchs, Meadows told her they had "a good meeting" and that whatever information she was able to provide to him, he would report back to Trump.
Raffensperger announced on Dec. 14 that Cobb County would conduct a signature audit, saying there were specific and credible allegations that signature matching wasn't done properly by election officials in the June primary.
A total of 15,118 absentee ballot oath envelopes, which is where voters sign, were randomly selected to be audited.
The audit was completed on Dec. 29, and investigators only found two ballots that should not have been accepted as they were. In Georgia, absentee by mail voters have the opportunity to cure a deficient absentee ballot, and the GBI said that these ballots should have gone through that process.
But the investigators also determined that neither of these ballots were fraudulently cast.
"I would also note for the record as well that during the course of the audit, there were no fraudulent absentee ballots identified in the process," GBI Director Vic Reynolds said in a press conference on Dec. 30.
In one instance, the voter's spouse signed the oath envelope on the voter's behalf; in the other, the voter signed the oath envelope in the wrong place.
In both cases, the audit team was able to contact both voters and confirm they had filled out their respective ballots themselves, Reynolds said.
The video in the media player above was used in a previous report.