The House Democrats prosecuting the impeachment of President Trump Donald John TrumpObama calls on Senate not to fill Ginsburg's vacancy until after election Planned Parenthood: 'The fate of our rights' depends on Ginsburg replacement Progressive group to spend M in ad campaign on Supreme Court vacancy MORE are planning a marathon preparation session ahead of next week's Senate trial, using the long holiday weekend to polish their case that the president abused his power in his dealings with Ukraine.

The seven impeachment managers tapped to make the Democrats' case before the Senate will return to Washington on Sunday to dig through the extensive record built over the course of the months-long investigation that led to Trump's impeachment last month, according to aides working on impeachment.

They'll be joined by staffers and counselors for the Intelligence, Judiciary and Oversight committees, all working to "refine" their arguments before taking their case to the Senate trial, with launches in earnest on Tuesday. The extensive preparations will include a walk-through of the Senate chamber.

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"The case is not a complicated one," said one Democratic aide working on the process. "The safety and security of the United States, of our Constitution ... [and] our democracy domestically rests on elections. And when the president invites a foreign government to announce investigations attacking a political opponent, he's undermining our democracy."

Aside from the legal merits of the case, much of the Democrats' argument will also delve into process.

Senate Majority Leader Mitch McConnell Addison (Mitch) Mitchell McConnellObama calls on Senate not to fill Ginsburg's vacancy until after election Planned Parenthood: 'The fate of our rights' depends on Ginsburg replacement Progressive group to spend M in ad campaign on Supreme Court vacancy MORE (R-Ky.) has resisted the notion of considering any evidence, or hearing witness testimony, outside of that examined in the House investigation. That position has gained outsize prominence — and stirred outsize controversy — with the emergence of beguiling new details surrounding Trump's efforts to press Ukrainian leaders to find dirt on his political opponents.

In recent days, Democrats have received a trove of documents from Lev Parnas, a Soviet-born Florida businessman and close associate of Trump's personal lawyer, Rudy Giuliani Rudy GiulianiGrand jury adds additional counts against Giuliani associates Lev Parnas and and Igor Fruman Juan Williams: Breaking down the debates Giuliani criticizes NYC leadership: 'They're killing this city' MORE, who led the pressure campaign on Ukrainian officials. Parnas, who was on the front lines of the unsuccessful effort to launch the Ukrainian investigations, has alleged that Trump was privy to that campaign from the start, along with other top administration officials that include Vice President Pence, Attorney General William Barr Bill BarrBarr says Ginsburg 'leaves a towering legacy' Republicans call for DOJ to prosecute Netflix executives for releasing 'Cuties' Trump doesn't offer vote of confidence for FBI director MORE and Secretary of State Mike Pompeo Michael (Mike) Richard PompeoHouse panel halts contempt proceedings against Pompeo after documents turned over Outgoing ambassador to China slams Beijing over coronavirus: 'Could have been contained in Wuhan' Hillicon Valley: FBI chief says Russia is trying to interfere in election to undermine Biden | Treasury Dept. sanctions Iranian government-backed hackers MORE.

"President Trump knew exactly what was going on," Parnas told MSNBC's Rachel Maddow Rachel Anne MaddowMichael Cohen: Trump hates Obama because he's everything he 'wants to be' The Hill's 12:30 Report - Presented by Facebook - Trump floats 0M+ in personal spending for reelection bid Feehery: Unconventionally debunking the latest political conventional wisdom MORE this week.

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Trump has denied any association with Parnas, while attacking the Democrats' impeachment effort as a politically motivated "hoax."

Democrats have also found ammunition in John Bolton John BoltonDiplomacy with China is good for America The Hill's Morning Report - Sponsored by The Air Line Pilots Association - Pence lauds Harris as 'experienced debater'; Trump, Biden diverge over debate prep DOJ launches probe into Bolton book for possible classified information disclosures MORE, Trump's former national security adviser, who had refused to testify in the House investigation but is now offering his insights under Senate subpoena.

McConnell has agreed to Senate rules allowing votes on potential witnesses, but not before the Democrats make their opening arguments and Trump's defense team offers its rebuttal. That chronology has outraged Democrats, who want all the evidence presented at the outset of the debate.

"When in a trial do you address witnesses' testimony at the end of the trial and not at the beginning?" a second Democratic aide told reporters Friday evening. "We're talking about specific witnesses, and specific documents from specific agencies that the president has acted to blockade from Congress and to suppress."

While House investigators heard testimony from 17 diplomats and national security officials with experience in Ukrainian affairs, at least a dozen others obeyed a White House directive to refuse participation in the process. Separately, the administration, defying House subpoenas, rebuffed all Democratic requests for documents related to the Ukraine episode.

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Democrats have pounced on the White House recalcitrance to hammer McConnell's argument that he's simply conducting the process according to the same parameters that governed President Clinton's impeachment trial in 1999. Then, the Democrats note, the president allowed all requested witnesses to testify, while providing tens-of-thousands of pages of documents to the special prosecutor managing the investigation. Additionally, three witnesses who had previously testified in the special prosecutor's probe into Clinton were interviewed again during the Senate trial — a process backed by Republicans, including McConnell, at the time.

"There was no argument about documents in Clinton because President Clinton had provided those 90,000 documents. How many documents has President Trump provided in response to House subpoenas? Zero," said the first Democratic aide. "We ought to start with that right away. It speaks to the fundamental fairness of the trial, and it is out of sync with precedent, with law and with what the American people want."

Democrats are also wary that the administration's blanket withholding of related documents gives Trump a wild card in the coming fight. They're voicing concerns that the president's defense team will try to slip some of that evidence into the trial, cherry-picking only the documents that boost Trump's case.

"One thing we'll be watching very closely is whether the president is seeking to game the system by selectively introducing documents or [other] material here and there in order to suggest a misleading narrative," said the second Democratic aide. "That's something we're very keenly aware of."

The release of documents from both sides ahead of the Senate trial will follow two streams in the coming days. The Democratic impeachment managers, led by Intelligence Committee Chairman Adam Schiff Adam Bennett SchiffTop Democrats call for DOJ watchdog to probe Barr over possible 2020 election influence Overnight Defense: Top admiral says 'no condition' where US should conduct nuclear test 'at this time' | Intelligence chief says Congress will get some in-person election security briefings Overnight Defense: House to vote on military justice bill spurred by Vanessa Guillén death | Biden courts veterans after Trump's military controversies MORE (D-Calif.), presented their articles to the fully packed Senate on Thursday. Trump's team is slated to provide their response to those charges on Saturday at 6 p.m., and Democrats will then offer their own formal counter-argument to the administration at noon on Monday.

Separately, House Democrats will release their trial brief on Saturday at 5 p.m. That will be followed by the president's trial brief, due Monday at noon. Democrats will then have exactly 24 hours to formulate their response to the White House brief.

Meanwhile, Democrats on the House Judiciary Committee on Friday posted all the information that will be transmitted to the Senate as part of the trial, including all the closed-door depositions, public hearing transcripts, notices of those witnesses who refused to testify, and supplemental information that includes the recent trove of photos and documents provided by Parnas.

Despite McConnell's resistance to hearing evidence that wasn't presented during the House investigation, Democrats say they're ready to lean on that supplementary information as they make their oral arguments before the Senate. If the majority leader intends to follow the Clinton model, they argue, that evidence should be permitted.

"The House Judiciary Committee ... can produce the record which will consist of publicly available material," said the first Democratic aide, citing the Clinton rules. "There is no reason why the same that precedent should not apply. We fully expect that it will apply. And if it does not apply, you'll hear about it from us."