Gerry Adams told Bill Clinton he would take steps to ensure David Trimble was "okay" and could sell a deal to the Ulster Unionists which would see the establishment of an executive after the signing of the Good Friday Agreement.
The revelation comes as details of phone calls from former US president to British prime minister Tony Blair and various Irish politicians are made public.
The transcripts, along with a number of briefing papers, cover the period between 1998-2000 have been released to the Irish Times by the Clinton Presidential Library in Little Rock, Arkansas.
Collectively they illustrate Bill Clinton's deep involvement in the fledgling peace process and efforts to establish a devolved executive.
In one extract from June 1999, as moves to form an executive are frustrated by wrangling over IRA decommissioning, the president calls Ulster Unionist leader David Trimble assuring him that he is available to speak "in the middle of the night" if need be.
"I can do or say that will either help you with your own people by showing the United States will give you the high ground by completely disavowing the other side if they don’t keep their word, or if you can think of anything I can do to persuade Sinn Féin to come closer to you," he told Trimble.
"I will do that. I know what position you are in."
"I will try not to disturb your sleep," the UUP leader responds, "but I thank you very much for this call."
Ensuring Trimble can keep hardliners in his party at bay became a key concern for all involved.
Clinton told Adams: "In the end, Gerry, no matter what Tony does or what I say, Trimble, to get a deal, is going to have to take some risks. You are going to have to take a world of crap. We can’t immunise him from all that risk. You can be neutralised, but he can be deposed."
In a later conversation where discussions centre on the sequencing of declarations and events which would allow the executive to be formed, the president and the Sinn Féin leader discuss whether Trimble will go for the deal.
"I think he is going to do it. I’ll bet you a dollar he goes for it," Adams says.
"That is a dollar I would love to pay off," Clinton replies.
The Sinn Féin leader then suggests he can help smooth the way for his UUP counterpart to ensure a deal is possible but does not state explicitly what he will do.
"It sounds silly and I couldn’t say to him like I can to you, but we’ll make sure he’s okay,” Adams says. "I look forward to taking your money."
Notably, Trimble told Clinton hours later that he cannot do a deal that day but is hopeful that his party can be brought on board in the coming days and weeks.
Clinton was keen to assure the future first minister that they will stand by him.
Referring to Sinn Féin, the president said: "Personally, if they screw us on this, I will support kicking them out and stand up publicly and say that you are not to blame and they are."
He also offers to call unionists – such as Reg Empey and Jeffrey Donaldson – who have opposed Sinn Féin’s entry into government.
"You’re a good man, David. You’ve made decommissioning real," Clinton tells him.
Eleven months later, after the Ulster Unionists back a package of proposals, including the IRA’s promise to decommission, to reinstate the power-sharing institutions, the president calls Gerry Adams to congratulate him.
"I hated to see Trimble have to go back to all his crazies, but it came out okay," Clinton tells the Sinn Féin leader.
“Once again we are at this point because of your unique understanding,” Adams tells him. “I have been saying to people: let’s make sure we get as much progress as we can while you are in the White House. It’s no accident that this has happened during your presidency. Thanks again.”
