House Democrats launched their final round of arguments in President Trump Donald John TrumpUS reimposes UN sanctions on Iran amid increasing tensions Jeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Trump supporters chant 'Fill that seat' at North Carolina rally MORE’s impeachment trial on Friday, shifting their focus to the president’s blanket stonewalling of Congress’s inquiry into his Ukrainian affairs as another basis for his removal from office.

Democrats say Trump trampled on Congress’s legal authority to act as a check on presidential power when he adopted an across-the-board refusal to cooperate with House investigators examining his dealings with Ukraine last year.

While their case has centered on allegations that Trump abused his power, the third and final day of the Democrats’ opening arguments will focus on the second impeachment article passed by the House last month: obstruction of Congress.

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House 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.), the lead manager of the House team, also signaled that Democrats intend to put up a fight Friday for witnesses, pushing back on the White House legal team’s claims of executive privilege.

“This is not a trial over a speeding ticket or shoplifting. This is an impeachment trial involving the president of the United States,” Schiff told reporters in remarks ahead of Friday’s arguments.

“Unlike in the House where the president could play rope-a-dope in the courts for years, that is not an option for the president's team here,” he continued. “And it gives no refuge to people who want to hide behind executive privilege to avoid the truth coming out.”

The Democrats’ impeachment case hinges on allegations that Trump withheld military aid to Ukraine, not to advance U.S. interests, but as leverage to pressure the country’s leaders to find dirt on his political opponents.

“No one anticipated that a president would stoop to this misconduct, and Congress has passed no specific law to make this behavior a crime,” House Judiciary Committee Chairman Jerrold Nadler Jerrold (Jerry) Lewis NadlerSchumer: 'Nothing is off the table' if GOP moves forward with Ginsburg replacement Top Democrats call for DOJ watchdog to probe Barr over possible 2020 election influence House passes bill to protect pregnant workers MORE (D-N.Y.) said Thursday. “Yet this is precisely the kind of abuse that the Framers had in mind when they wrote the impeachment clause.”

Trump has dismissed the allegations for months, saying his interactions with Ukrainian leaders were “perfect” and accusing Democrats of conducting a “witch hunt” designed solely to damage his reelection prospects in November.

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“The Do Nothing Democrats just keep repeating and repeating, over and over again, the same old ‘stuff’ on the Impeachment Hoax,” Trump tweeted Friday morning.

The president’s legal team, which will begin its arguments on Saturday, has said both impeachment articles are illegitimate, not least because neither charge represents a specific violation of federal law. The obstruction allegation is “absurd,” his lawyers have added, because it ignores the president’s authority to invoke special executive powers protecting sensitive internal deliberations.

Democrats argue the president’s decision to block witnesses not discretely, but by asserting “absolute immunity,” prevented them from gaining access to key testimony from officials with first-hand accounts of Trump’s contacts with Ukraine.

“The Framers, the courts, and past Presidents have recognized that honoring Congress’s right to information in an impeachment investigation is a critical safeguard in our system of divided powers,” the Democratic impeachment managers wrote in the 46-page brief outlining their legal arguments heading into the Senate trial.

The administration’s defiance came in two forms. First, the White House directed administration officials not to testify in the investigation, even if subpoenaed. And second, the administration refused to turn over any documents related to Trump’s pressure campaign in Ukraine.

The stonewalling was only partially successful: Democrats secured the testimony of 17 officials with a window into the Ukraine affair, many of whom appeared under subpoena.

But at least 12 others refused to cooperate, including former national security adviser 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, acting White House chief of staff Mick Mulvaney Mick MulvaneyMick Mulvaney to start hedge fund Fauci says positive White House task force reports don't always match what he hears on the ground Bottom line MORE, and two officials at the Office of Management and Budget (OMB) who are said to have insights into Trump’s decision to withhold the military aid.

The question of whether the Senate will compel their testimony has emerged as one of the central battles throughout this week’s trial. Behind Senate Majority Leader Mitch McConnell Addison (Mitch) Mitchell McConnellMomentum growing among Republicans for Supreme Court vote before Election Day Trump expects to nominate woman to replace Ginsburg next week Video of Lindsey Graham arguing against nominating a Supreme Court justice in an election year goes viral MORE (R-Ky.), most Republicans have rejected the idea of allowing new witnesses or material evidence, maintaining it was the job of the House, not the Senate, to do the investigating.

But the arrival of new evidence, combined with Bolton’s offer to testify under subpoena, has put fresh pressure on GOP leaders to consider information not available to House impeachment investigators last year.

“If the president believes he did nothing wrong, that everything's perfect, he should have nothing to fear from these witnesses and documents,” Senate Minority Leader Charles Schumer Chuck SchumerVideo of Lindsey Graham arguing against nominating a Supreme Court justice in an election year goes viral Graham signals support for confirming a Supreme Court nominee this year Pelosi orders Capitol flags at half-staff to honor Ginsburg MORE (D-N.Y.) said Friday morning.

Republicans have shot back, saying Democrats should have waited for the courts to resolve the disputes over witnesses and documents before voting on their impeachment articles last month.

Democrats say they couldn’t wait months or years for courts to act, since their central allegation maintains he was trying to “cheat” in November’s election.

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“Impeachable offenses involve wrongdoing that reveal the president as a continuing threat if he is allowed to remain in office,” Nadler said.

Democrats have described the administration’s lack of cooperation as nothing less than an attempt to coverv up for the president’s conduct.

But the White House has described it as more a political response: Democrats are seeking to damage Trump’s presidency in an election year.

And it wouldn’t be the first time that charge has emerged. Trump's allies note that the president has faced most of his time in office being investigated, as Democrats cheer on the inquiries.

Trump allies will point to former special counsel Robert Mueller Robert (Bob) MuellerCNN's Toobin warns McCabe is in 'perilous condition' with emboldened Trump CNN anchor rips Trump over Stone while evoking Clinton-Lynch tarmac meeting The Hill's 12:30 Report: New Hampshire fallout MORE’s report that found no evidence of coordination between the Trump campaign and Russia — though he did not make a determination either way on whether Trump obstructed justice.

But Democrats warned that Trump is setting a dangerous precedent, stealing congressional powers that would act as a check on future presidents.

“In terms of the obstruction, the precedent would be equally devastating to the government because it would mean that the impeachment power is essentially a nullity. It is unenforceable. The president can delay it into nonexistence and this goes not just to impeachment investigations,” Schiff said.

“If the Senate goes along with the president's obstruction, it will in every way impede the House and impede the Senate in its own responsibilities."