By Richard Cowan
WASHINGTON (Reuters) - John Bolton meet Monica Lewinsky.
Twenty-one years ago former White House intern Lewinsky was at the center of a tug-of-war over whether she would testify in the U.S. Senate impeachment trial of President Bill Clinton, a Democrat.
Now it is Bolton, fired last September from his job as White House national security adviser, who is the potential prize witness in Republican President Donald Trump's impeachment trial. Democrats believe he possesses damaging information and want him to testify, while many Republicans, who control the Senate, do not want to hear from him.
In many ways, the two impeachment cases could not be more different.
In 1999 the allegations centered on whether Clinton lied under oath about a sexual act with Lewinsky, while now Trump has been charged with abusing his power by pressing a vulnerable ally Ukraine to investigate a potential November election opponent, Joe Biden.
But fear is a common factor. Some Trump allies worry that new witness testimony televised live from the Senate floor could undermine his defense that he did nothing wrong.
Former lawmakers and aides who played key roles in Clinton's impeachment trial recalled in interviews with Reuters many of the same tensions and fears that are playing out today.
"The thing we went to work every morning worrying about until we went home at night was whether we can hold the Democrats" in the Senate in their support of Clinton, recalled Doug Sosnik, who was a senior adviser to the president for most of his eight years in office.
The top Republican in the Senate, Mitch McConnell, says that he wants to follow the same initial procedures that were used in the Clinton trial, which were adopted unanimously by both parties.
What is left unsaid is that the most contentious issue now - the calling of witnesses - was also the most contentious issue then and was not resolved until well into the trial.
As the second impeachment trial in U.S. history was about to begin in January 1999, senators were at an impasse over the question of witnesses.
"There were people who strongly believed Bill Clinton should be removed from office. They wanted Monica Lewinsky to come to the Senate chamber to be questioned as a witness," then-Senator Byron Dorgan, a Democrat who retired in 2010, said.
The White House and Senate Democrats feared that then-Senator Joseph Lieberman, a moderate Democrat who had expressed particular disgust at Clinton's behavior, could bolt and bring some additional Democrats with him to vote to convict Clinton.
Senators locked themselves inside the Old Senate Chamber where the Senate conducted business from 1810 to 1859, while liberal Senator Ted Kennedy and conservative Senator Phil Gramm helped to forge a compromise.
Under the deal, the trial would begin with House of Representatives Republicans presenting their case against Clinton, followed by a rebuttal by Clinton's lawyers. Senators could then question the two sides.
Only then would senators hash out whether witnesses would testify. Later, in partisan votes in the Republican-controlled Senate, it was decided that neither Lewinsky nor anyone else would testify in the chamber. Instead, private videotaped depositions of Lewinsky and two Clinton aides would be recorded.
"In my Senate tenure, I have not seen a more contentious issue than the calling of witnesses either live or videotaped," longtime Senator Arlen Specter later said in a Senate speech.
"I understand why the president's counsel had fought so strenuously to keep her away from the well of the Senate," said Specter, who died in 2012. "Had she told her whole story in the well of the Senate, a rapt national TV audience would have been watching and the dynamics of the proceeding might have been dramatically changed."
Specter's comments underscore why some Republicans today may be anxious to ensure that Bolton does not testify on the Senate floor. Democrats say Bolton could provide a first-hand account of important discussions regarding Ukraine in the White House.
In a telephone interview with Reuters from his home state of Texas, Gramm said he did not believe there was even a need for witnesses in Trump's trial.
"Nobody disputes the fact that the president (Trump) made the (telephone) call" to Ukraine President Volodymyr Zelenskiy to investigate Biden, Gramm said.
While most Republicans publicly dispute that Trump was seeking a personal favor from Zelenskiy, Gramm insisted, "Nobody disputes the fact that when a president asks you to do something, there's some pressure involved."
Gramm did not say whether he thought Trump should have been impeached for that, adding it is not his battle.
Democrats argue that unlike in the Clinton case a number of the witnesses they want to hear from have not already testified to the House of Representatives impeachment inquiry or in other legal proceedings.
Democratic Senator Dick Durbin, who in 1999 voted to acquit Clinton, said, "Most of these Republican senators are dismissing the whole (impeachment) effort. They may have second thoughts if new witnesses come forward."
A senior Republican, Senator John Cornyn, however, warned in December of the "unintended consequences" of having witnesses.
"Witnesses say the darndest things," he said.
In 1973, a former White House aide named Alexander Butterfield told a Senate committee about the existence of an Oval Office taping system. It was a seminal moment in the investigation of President Richard Nixon's involvement in a break-in of a Democratic National Committee office, which ultimately drove him from office before he could be impeached.
(Reporting by Richard Cowan, editing by Ross Colvin and Grant McCool)