(CNN) As special counsel Robert Mueller's office circles around a possible interview with President Donald Trump, there's a clear road map to how Trump's negotiations could evolve.

That guide comes from decades-old court records that CNN has reviewed . The documents available, though they may be incomplete, show how Whitewater independent counsel Ken Starr forced a grand jury appearance from President Bill Clinton.

They indicate that if Trump's team follows a similar legal approach, the negotiations could last months and his interview with Mueller may be inevitable.

Negotiations between the Clinton and Starr teams lasted six months, and took more than a dozen lawyers' letters, a subpoena and a court hearing before Clinton sat for the interview. At no time did Starr's investigators tell Clinton's team he was the target of their investigation. Yet with hindsight, the documents available through Starr's report to Congress make it plain Clinton was in the independent counsel's crosshairs as the grand jury sought the President's testimony. Clinton's response was to delay and deny.

Mueller has been investigating possible collusion between the Trump campaign and Russians, and made clear to the President he would like an interview. The Mueller team has used some of its recent interviews with senior administration officials to ask about Trump's firing of FBI Director James Comey, a possible question of obstruction of justice. The counsel's office has not announced new cases from the investigation since former national security adviser Michael Flynn pleaded guilty to lying to investigators December 1.

Since then, Trump's personal lawyers have discussed the possibility of an interview with Mueller. While Trump has said publicly he'd speak with the special counsel, his legal team has coalesced around telling Mueller no.

Trump's personal lawyers haven't received requests in writing for Trump's testimony. Once a request comes in writing, Mueller's office will have upped the pressure just like Starr's team did to Clinton.

This is a retelling of Clinton's testimony negotiation, as captured in the communications between Starr's deputy independent counsel Robert Bittman and Clinton's personal criminal defense attorney David Kendall throughout 1998.

Bittman's law firm, McGuireWoods, currently represents Vice President Mike Pence in the Russia investigation, and Kendall still represents Bill and Hillary Clinton. Both Bittman and Kendall declined to comment for this story.

The cases involving Starr's subpoenas are still sealed in the US District Court for the District of Columbia Circuit, though some of the court documents are available through Starr's report to Congress in September 1998.

CNN on Friday asked the federal court to unseal those cases to obtain the full records.

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How it started

Twenty years ago this month, Bittman, the prosecutor, wrote to Clinton's lawyer with a reminder and an invitation.

"President Clinton has publicly pledged to cooperate fully with the investigation involving Monica Lewinsky," Bittman began, according to his February 2, 1998, letter. Clinton had been invited in late January to testify before a federal grand jury reviewing the Lewinsky case. Kendall hadn't responded. "The grand jury awaits the President's decision," Bittman wrote.

Two days later, Clinton's lawyer had declined the invitation. So Bittman wrote again, with another invitation, for Clinton to testify in mid-February. Again, Kendall did not respond.

"Let me make our request specific and clear: the grand jury deserves to know whether the President will respond, favorably, to the invitation. Such an invitation is, of course, fully consistent with our profound respect for the Presidency in our system of separated powers," Bittman wrote in another letter, according to the Starr investigation files.

This time Clinton's lawyer wrote back. He had reasons Clinton simply could not find the time. "The situation in Iraq continues to be dangerously volatile," he began, then cited Clinton's "heavy travel schedule." Kendall asserted he had not had the opportunity to prepare his client for a grand jury appearance.

Clinton still 'extraordinarily busy'

As February turned to March, Starr's office made its third and fourth written requests for Clinton to testify voluntarily.

"In regard to the various explanations you have been kind enough to advance for declining our four invitations, I note that the state visit of Prime Minister [Tony] Blair has passed; the 'situation in Iraq' has, thankfully, eased; and you have now had some six weeks to 'prepare' the president." Bittman continued: "The President has -- with all respect -- found time to play golf, attend basketball games and political fundraisers, and enjoy a ski vacation. We assure you that the grand jury's inquiry of the President will not take long."

Clinton's lawyer delayed yet again, with a hand-delivered letter to Starr's office citing Clinton's "extraordinarily busy" schedule.

Bittman's next letter reminded Kendall of how Clinton had been deposed in other aspects of the Whitewater case, and even testified as a defense witness in two trials in Arkansas. The prosecutor closed his March 13, 1998, request with a reminder that the independent counsel worked on behalf of the grand jury, and that "nothing, in short, should stand in the way of the truth's coming out."

Kendall's reply took on a more biting tone. He reminded the independent counsel how Clinton had submitted written answers to questions from the prosecutors and turned over more than 90,000 documents.

The Trump team now stands in a similar place. As of late January, Trump's personal lawyers have turned over more than 20,000 White House documents and 1.4 million pages of campaign documents. They've allowed 20 White House staff members and 28 campaign staffers and others to sit for voluntary interviews.

At this time, Trump's negotiations still focus on a voluntarily interview with the special counsel, instead of sworn testimony before the grand jury, which would be a more serious arrangement, according to CNN reporting.

Kendall's last letter declining an interview landed in Starr's office in mid-April 1998. By that time, Lewinsky was cooperating with prosecutors. Then, both sides went silent for exactly three months, according to the Starr investigation records.

The White House received a grand jury subpoena for Clinton's testimony on July 17, 1998.

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Now faced with an official demand, Clinton's lawyer reverted to the same tactic he had used over the previous six months: stalling.

"The President is willing to provide testimony for the grand jury, although there are a number of questions relating to the precise terms and timing which must be worked out," Kendall wrote to Bittman, asking the independent counsel to withdraw the subpoena.

A subpoena that would force the grand jury testimony of a sitting president was a significant change in their negotiation's tenor, a legal demand never used before for the nation's chief exeuctive.

A subpoena of a president posed "grave and literally unprecedented constitutional questions," Kendall wrote. He argued that targeting the president in an investigation violated the separation of powers, and that the president was exempt from the typical criminal process, a similar set of arguments to what legal scholars have discussed regarding Trump and obstruction of justice.

Meeting the judge

Clinton's team said it was prepared to fight over the constitutional disagreement.

That's when Starr's prosecutors and Clinton's lawyers went to court. The then-chief judge of the federal district court in Washington, Norma Holloway Johnson, held a hearing on July 28 to decide if Clinton's legal team could delay further. The constitutional issues Kendall had mentioned weren't on the table that day; the President's lawyer said he would avoid litigating them in that hearing.

The judge listened to both sides, and told the lawyers she realized the grand jury had heard testimony about Clinton's relationship with Lewinsky.

"Now, maybe they don't have any legal right to hear from the President. Maybe that is an issue we will have to resolve before this subpoena can be honored. But what we need to do, I think, is to move forward, and move forward expeditiously," she said. The judge ended the hearing without making a decision.

Before she could write one, Clinton agreed to testify -- from the White House, with his lawyers present, on a closed-circuit video that the grand jury would watch -- on Aug. 17, 1998.