The White House argued in a legal brief filed Monday that the two articles of impeachment against President Trump are “structurally deficient,” decrying a “rigged process” and urging senators to “immediately” acquit the president of the charges that will be formally presented at his trial that starts in earnest this week.

The filing came as the House’s designated impeachment managers and Trump’s legal counsel conducted final preparations ahead of the trial proceedings that will begin Tuesday, marking the substantive start of just the third Senate trial of a U.S. president in history. On the Republican side, Senate Majority Leader Mitch McConnell (R-Ky.) circulated ground rules for a rapid trial, while Senate aides and GOP lawyers were also weighing contingency plans in case Democrats are successful in forcing witnesses to testify.

Trump’s legal team, led by White House counsel Pat Cipollone, wrote that Trump “did absolutely nothing wrong” as it accused the House Democrats who impeached the president of attempting to overturn the results of the 2016 election and “to interfere in the 2020 election.”

Harvard law professor emeritus Alan Dershowitz spoke Jan. 19 about his role on the president's legal team after Trump picked him, personally. (The Washington Post)

“The only threat to the Constitution that House Democrats have brought to light is their own degradation of the impeachment process and trampling of the separation of powers,” Trump’s lawyers wrote in the 171-page legal brief. “Their fixation on damaging the President has trivialized the momentous act of impeachment, debased the standards of impeachable conduct, and perverted the power of impeachment by turning it into a partisan, election-year political tool.”

Some of the preparations Monday came in the form of walk-throughs of the Senate chamber by both sides, scoping out the surroundings that will house all 100 senators for hours of opening arguments and questions in Trump’s impeachment case over the next several days.

But the two sides also spent Monday previewing the case they’ll make on the Senate floor through dueling filings and efforts to refute the other side’s arguments about whether Trump’s attempts to pressure Ukraine amount to impeachable conduct. Both the Democratic House managers and Trump’s legal team are battling to persuade a small group of swing GOP senators who will decide whether they will need additional witnesses and evidence to determine Trump’s fate.

McConnell’s organizing resolution, which he circulated late Monday afternoon, offers each side 24 hours to make its opening arguments, starting on Wednesday but compressed into two session days. It is unclear whether Democrats would press to use all their time, which could push testimony past midnight.

After the House managers and Trump’s lawyers make their case, senators will be allowed 16 hours to question the opposing sides.

After that, the sides will debate for a maximum of four hours on whether to consider subpoenaing witnesses or documents at all, followed by a vote on whether to do so. If a majority of senators agree, then there will probably be motions from both sides to call various witnesses, with subsequent votes on issuing subpoenas.

The resolution also allows Trump’s team to move to dismiss the charges at any time — although it is not explicitly mentioned in the four-page measure — because doing so is allowed under standard impeachment trial rules. The Senate trial also won’t automatically admit evidence from the House process, according to GOP officials, a key difference from the impeachment trial of President Bill Clinton more than two decades ago. Though the material will be printed and made available to senators, it won’t be automatically admissible unless a majority of senators approve it.

The resolution infuriated Democratic senators, with Senate Minority Leader Charles E. Schumer (D-N.Y.) calling the document a “national disgrace” and accusing McConnell of shrouding testimony and rushing the trial.

“We are gratified that the draft resolution protects the president’s rights to a fair trial, and look forward to presenting a vigorous defense on the facts and the process as quickly as possible, and seeking an acquittal as swiftly as possible,” said Eric Ueland, the White House’s director of legislative affairs.

The administration laid out two main points as it seeks a quick acquittal for Trump: that the articles of impeachment are “deficient” because they don’t involve any violations of law, and that the House’s charge of obstruction of Congress will damage the constitutional separation of powers.

House Democrats — in a separate filing that was also due Monday — disputed the White House’s argument, asserting that abusing the powers of his presidency was an impeachable offense and that Trump was the “Framers’ worst nightmare come to life.”

The White House’s legal brief submitted to the Senate — offering the first detailed glimpse into its defense against the two impeachment charges — was adamant that Trump did nothing wrong, deploying a legalese version of the scorched-earth rhetoric commonly used in the president’s Twitter feed. One Democratic aide working on the impeachment trial, who spoke to reporters in a briefing on the condition of anonymity, likened the brief to an “extremely extended version of a presidential tweet.”

The proceedings Tuesday will formally begin with a debate over the McConnell resolution. The impeachment managers and the president’s lawyers will have an opportunity to debate the proposed rules, while Schumer is expected to offer changes to the measure that would allow the Senate to call several witnesses desired by Democrats at the outset. Democrats could also push for more than one vote on witnesses and documents.

But all 53 Republican senators are expected to support the rules as written by McConnell. Once those parameters are set, the formal arguments will begin.

After spending several hours in a nearly empty Capitol, holding talks with staff on the trial resolution, McConnell left at 7 p.m. Monday, saying the final touches were now in place.

“As you can imagine, we’re discussing getting ready for tomorrow. And we’ll be ready to go,” he told reporters, indicating he had no real discussions with Schumer about how Democrats would fight the resolution. “That’s a good question to ask him.”

In their own 111-page brief filed Saturday, the House’s seven impeachment managers laid out their case against Trump that they will present to senators, arguing that the president’s conduct posed a national security threat and that he obstructed congressional efforts to obtain testimony and documents about his dealings toward Ukraine.

The House’s legal brief reiterated many of the findings and arguments that Democrats have made for months — including allegations that Trump withheld nearly $400 million in military aid for Ukraine and a coveted White House meeting with its leader, Volodymyr Zelensky, to pressure the country into conducting investigations into former vice president Joe Biden and his son Hunter.

The president’s lawyers argued in their filing, however, that House Democrats had no evidence to back up its accusation that Trump conditioned the aid and the White House visit on an investigation into a political rival. The attorneys also defended Trump’s conduct, saying a July 25 call between Trump and Zelensky that is at the heart of the House’s impeachment case was “perfectly appropriate” and that the Ukrainian leader has not indicated any impropriety with the conversation.

The lawyers pointed to a rough transcript of the call as proof that Trump did not seek a quid pro quo in his request for the probe of the Bidens and of a debunked theory alleging Ukrainian interference in the 2016 election.

In the call, Trump told Zelensky that “I would like you to do us a favor though because our country has been through a lot and Ukraine knows a lot about it.” Those favors do not involve Trump’s personal interests, argued the White House lawyers, who added: “The President cannot be removed from office because House Democrats deliberately misconstrue one of his commonly used phrases.”

That transcript of the call, Trump’s lawyers also said, shows that the president was speaking about issues of burden-sharing among European nations as well as corruption — two foreign policy issues that not only were in his purview as commander in chief but reflected his “longstanding concerns” about foreign aid.

The lawyers said it would have been “appropriate” and “entirely proper” for Trump to ask Zelensky about those issues, including about Hunter Biden, who served on the board of Burisma, Ukraine’s largest private gas company, whose owner came under scrutiny by Ukrainian prosecutors for possible abuse of power and unlawful enrichment. Biden was not accused of any wrongdoing.

In response to the White House’s argument that there was no underlying crime, Democrats are likely to cite an opinion issued after Trump’s impeachment from the Government Accountability Office that the administration’s withholding of aid was a violation of law. Trump’s legal team is expected to argue that senators must focus solely on the information relied upon by the House in its Dec. 18 vote to impeach the president.

As for the obstruction-of-Congress charge, the president’s legal team called it “frivolous and dangerous” because Trump had the right to assert certain executive branch privileges.

“Accepting that unprecedented approach [from Democrats] would fundamentally damage the separation of powers by making the House itself the sole judge of its authority,” the lawyers wrote in the brief. “It would permit Congress to threaten every President with impeachment merely for protecting the prerogatives of the Presidency.”

Earlier on Monday, the seven Democratic managers walked in procession, with their staff following behind, from the office of House Speaker Nancy Pelosi (D-Calif.) to the Senate chamber a few minutes after 11 a.m. Reporters were not allowed to view the walk-through, as the doors to the third-floor galleries above the Senate chamber were locked, and aides said the lawmakers would not discuss the visit.

Upon leaving, the managers slipped into a Rules Committee room near Schumer’s office. The area appears to be their workspace for the duration of the trial and was outfitted with two long tables — along which there are several computers set up — as well as a large elevated television screen.

House Judiciary Committee Chairman Jerrold Nadler (D-N.Y.) was not present for the managers’ meeting or the walk-through, though several of his staff were there.

Later Monday, the White House legal team conducted its own walk-through of the area. The president’s lawyers will have office space that is traditionally used by the vice president, a corner suite just off the floor in the reception room adjacent to the Senate chamber.

On the floor itself, each side will work from a specially designed set of tables that are curved in the arc of the well of the Senate, with the House managers on the Democratic side of the floor and Trump’s legal team on the GOP side.

The White House also announced late Monday that eight of the president’s most ardent House Republican defenders would join the impeachment team to “help expeditiously end this brazen political vendetta.” The GOP lawmakers include Reps. Douglas A. Collins (Ga.), Mike Johnson (La.), Jim Jordan (Ohio), Debbie Lesko (Ariz.), Mark Meadows (N.C.), John Ratcliffe (Tex.), Elise Stefanik (N.Y.) and Lee Zeldin (N.Y.).

Paul Kane contributed to this report.