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– On New Year's Day in 1999, Rep. Jim Sensenbrenner, R-Wis., sat on the floor of his Capitol Hill office, surrounded by piles of documents and legal notes, drafting his opening statement in President Bill Clinton's impeachment trial in the Senate.

With the sound of the University of Wisconsin Badgers facing off against the UCLA Bruins in the Rose Bowl blaring from a television in the background, Sensenbrenner readied his case that the president should be removed from office for lying about a sexual affair with a White House intern.

In the coming days, Speaker Nancy Pelosi, D-Calif., is expected to select four to 10 members of the House of Representatives for a similar assignment, making the case to the Senate for why President Donald Trump deserves to be ousted for pressuring Ukraine to investigate his political rivals. But unlike Sensenbrenner or the dozen other prosecutors who made the case against Clinton 21 years ago, the new prosecutors will not have had the benefit of a two-week holiday break to prepare their arguments or hone their strategies.

On Friday, after a weeks­long impasse, Pelosi alerted lawmakers that she would move next week to transmit the articles of impeachment to the Senate, prompting the start of a Senate trial as early as Wednesday.

Pelosi's decision to withhold the articles of impeachment in an unsuccessful effort to extract assurances from Senate leadership about the terms of the trial has delayed the appointment of the so-called impeachment managers, raising the stakes and compressing the timetable of their already challenging task.

It is a job that veterans say is fraught with legal complexity, political pressure and historic significance.

"I really don't want to give them any advice," Sensenbrenner said in an interview. "But I guess I can say that this is going to be a lot more work than you think."

"The American people," he added, "are going to be watching."

The pivotal role of the managers is one reason that Pelosi has waited to send the charges to the Senate. Sen. Mitch McConnell, R-Ky., the majority leader, said this week that he had the votes to move forward with an impeachment trial without committing to calling witnesses or hearing new evidence. Without knowing whether there will be witnesses to question or new complex documents to digest, the speaker cannot decide what kind of lawmakers are best suited to the task.

People close to Pelosi say it is all but certain that one of the managers will be Rep. Adam Schiff of California, a former federal prosecutor who oversees the Intelligence Committee and led the investigation into Trump's dealings with Ukraine. Rep. Jerrold Nadler of New York, chairman of the Judiciary Committee that approved the two articles of impeachment against the president that the House passed last month, is also widely expected to be a leader of the group.

Times have changed considerably since 1998, when the Republican-led House sent 13 white men to the Senate to serve as impeachment managers. Given the diversity of today's rank-and-file Democrats, Pelosi is likely to select a group to prosecute Trump that includes women and members of color.

Sensenbrenner had previously served as an impeachment manager in the case of Walter Louis Nixon Jr., a federal judge who was impeached and removed from the bench for lying to federal grand juries. In his preparation for the Clinton trial, Sensenbrenner recalled being given some wry advice from the House Judiciary Committee chairman at the time, Henry Hyde, R-Ill., who instructed him to keep his opening statement shorter than the two-and-a-half-day speech that kicked off President Andrew Johnson's impeachment trial in 1868.

Another Clinton impeachment manager, James Rogan, R-Calif., was chosen despite having just joined the House in 1997, in part because he had previously been a prosecutor, which had helped land him a seat on the Judiciary Committee.

Rogan was defeated by Schiff in 2000 and is now a state trial judge in California. A framed poster that hangs above the door to his judicial chambers in Orange County reminds him daily of the vitriol he attracted as one of Clinton's main antagonists. "People unite! DENOUNCE ROGAN!!!" it reads.

"I've been through one of these before," Rep. Steve Chabot, R-Ohio, one of the 13 Clinton impeachment managers, said at a hearing last month. "And they're ugly. So I have a lot of sympathy for the House managers that are going to be picked."

In the years since Clinton's trial, the job of the managers has only grown more complex. The debate is also more starkly partisan than it was then, with almost no defections from either side. Social media now allows for running commentary online, including by the president himself. During the House's impeachment inquiry, Trump used Twitter to disparage witnesses while they were testifying against him.

"They need to understand the seriousness of what they're going into," said Bill McCollum, a former representative from Florida who was one of the Clinton impeachment managers. "They're going to be doing something very unique — very few people have done what they're about to do."