When David Dorsen joined the Senate select committee on Watergate in 1973, it was less than a month before the panel's historic hearings began airing on national television.

President Richard Nixon with his edited transcripts of the White House Tapes subpoenaed by the Special Prosecutor, during his speech to the nation on Watergate, on April 29, 1974.

For lawyers like Dorsen, who stayed largely behind the scenes during the Senate probe, there was pressure not to just keep up with the pace of the investigation, but to make sure the right questions were asked of the right witnesses. The stakes were high as the staff looked into a matter as significant as potential wrongdoing by President Richard Nixon.

The time crunch was so tight that Dorsen at one point had to tell Sen. Sam Ervin, D-North Carolina—who chaired the select committee—that one of the hearings would have to be adjourned after opening statements. Lawyers weren't ready to question the witness.

"He forgot, and I had to remind everyone not to question him," Dorsen recalled. "As a professor might be one step ahead of his students, we were less than that ahead of the television."

Lawyers who have worked on past impeachment proceedings against Nixon and President Bill Clinton remember pressures like these from their time working on the inquiries. And they advise attorneys tasked with handling the impeachment inquiry of President Donald Trump to keep those demands in mind.

'Norms, Not Rules' Govern

Attorneys involved in impeachment proceedings for Nixon and Clinton said they had to essentially come up with procedures and legal arguments from scratch, as the last presidential impeachment was Andrew Johnson's in 1868.

U.S. President Donald Trump speaks during a news conference with Sauli Niinisto, Finland's president, not pictured, in the East Room of the White House on Oct. 2, 2019.  Photographer: Al Drago/Bloomberg

And as they found themselves in court, litigating issues like what evidence could be given to Congress, they created new road maps that have guided the way for future impeachment proceedings. But that doesn't mean the law surrounding impeachment is settled by any means.

"Whatever side you're on, you have to be very creative as a lawyer to make the most persuasive arguments," said Mark Alexander, dean of the Villanova University Charles Widger School of Law. "And there's a lot that's just not defined on impeachment."

As the House of Representatives embarks on its latest impeachment inquiry into Trump, attorneys emphasized the need for counsel on all sides to act thoroughly and methodically as they investigate allegations that Trump pressured Ukrainian authorities to investigate his political rival, former Vice President Joe Biden and Biden's son, Hunter.

Dorsen said staff working on Watergate went out of their way to track down all lines of inquiry—at one point even interviewing the Hollywood icon John Wayne after former White House counsel John Dean said he was asked to "do something" about an IRS audit of the actor.

While the Wayne audit ultimately didn't factor any further into their investigation, Dorsen said it was important for the committee to make sure it followed up on every potential act of presidential misconduct.

"We spent hundreds of hours literally searching for things like that, that never had an impact ultimately," Dorsen said. "But it's part of the job of an experienced investigator and prosecutor. I hope they know enough about that in the present setup to do the kinds of things that we did, whether they panned out or not."

Even with past examples to look back on, experts say there's plenty of legal territory on impeachment to explore. That includes how impeachment proceedings are conducted in the first place.