A flood of captivating new details surrounding 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's dealings with Ukraine has spilled out into the public just as the Senate begins the impeachment trial, putting fresh pressure on GOP leaders to consider witnesses and new documents.

The Government Accountability Office (GAO) on Thursday issued a stunning report, accusing the White House budget office of breaking the law by withholding military aid to Ukraine — the very issue at the heart of the Democrats' impeachment effort.

Separately, a close associate of 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, Trump’s personal lawyer, has delivered a trove of information to House Democrats related to Giuliani’s campaign to pressure Ukrainian leaders to find dirt on the president’s political rivals. Lev Parnas, a Soviet-born Florida businessman facing unrelated campaign-finance charges in New York, is also making the media rounds to deliver a damning message: Trump, he says, was privy to the pressure campaign from the start.

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“Every day new incriminating evidence comes forward,” Speaker Nancy Pelosi Nancy PelosiPelosi: Ginsburg successor must uphold commitment to 'equality, opportunity and justice for all' Bipartisan praise pours in after Ginsburg's death Pelosi orders Capitol flags at half-staff to honor Ginsburg MORE (D-Calif.) said Thursday at a press conference in the Capitol. “I think that only speaks very clearly to the need for the Senate to enter the documentation into their discussion."

The developments came just before the Senate accepted the two impeachment articles from House Democrats, who presented the charges on the Senate floor Thursday afternoon. The House passed the resolutions on Dec. 18, charging Trump with abusing his power in dangling military aid to secure political favors from Kyiv, then obstructing Congress as Democrats sought to investigate the matter.

Trump and his GOP allies have denied any wrongdoing, arguing the administration was simply ensuring that U.S. tax dollars were not frittered in a country long known for corruption. Behind 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.), GOP leaders have resisted the consideration of new evidence or witnesses in the trial phase, arguing the entire impeachment effort is merely a political scheme to hurt Trump’s reelection prospects in November.

"If the existing case is strong, there's no need for the judge and the jury to reopen the investigation,” McConnell said this week. “If the existing case is weak, House Democrats should not have impeached in the first place."

Yet the GAO, an independent government watchdog, found that the White House Office of Management and Budget (OMB) withheld the appropriated funds last summer — not as a programmatic delay but in order to advance the president’s own agenda, which violates a law that governs Congress's role in the federal budget process.

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“Faithful execution of the law does not permit the President to substitute his own policy priorities for those that Congress has enacted into law,” the report says. “OMB withheld funds for a policy reason, which is not permitted under the Impoundment Control Act (ICA). ... Therefore, we conclude that OMB violated the ICA.”

At a press conference in the Capitol Thursday, Pelosi read from the GAO report, then offered her own vernacular translation.

"The OMB, the White House, the administration broke — I'm saying this — broke the law,” she said. “This reinforces, again, the need for documents and eyewitnesses in the Senate."

The GAO report came on the heels of Parnas telling 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 on Wednesday night that Trump was aware of a scheme both to seek the removal of U.S. Ambassador to Ukraine Marie Yovanovitch and to create conditions to push Ukraine’s new president to announce investigations into former Vice President Joe Biden and his son Hunter Biden in order to help Trump’s 2020 reelection prospects.

House Democrats are seizing on the new developments to aid their calls for the Senate to provide a fair trial, which they say is contingent on being able to review new evidence and receive testimony from additional witnesses.

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“The additional documents and information about potential witnesses that have become available over the last several weeks only underscore the importance of a fair trial and a Senate that is open to hearing all of the evidence,” said 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.), who was tapped by Pelosi to lead the Democrats’ arguments in the Senate trial.

Still, Democrats won a near-term victory on Wednesday, when McConnell — who has been cold to the idea of calling any witnesses — agreed to a rules package that leaves open the potential for new witnesses to appear. Anything less, Democrats have charged, would be a dereliction of the Senate’s duty.

Democrats voted largely along party lines last month to impeach Trump on the two charges — abuse of power and obstruction of Congress — alleging that the administration dangled the promise of aid and a White House meeting as leverage for their investigation demands.

House Democrats charge that the White House then sought to obstruct their impeachment inquiry by blocking the testimony of current and former White House officials, while asserting absolute immunity over their testimony.

The OMB, however, is disputing the GAO opinion, arguing that the budget office used the “apportionment authority to ensure taxpayer dollars are properly spent consistent with the President's priorities and with the law."

Trump administration officials have argued they were seeking to ensure Ukraine was properly fighting widespread corruption, despite the Pentagon already certifying at the time of the delay that Ukraine had met the requirements set by Congress and after the agency notified Congress of its intent to release the funds.

On Thursday, a senior administration official called the GAO report an “overreach,” blasting the independent watchdog for getting involved “in the media's controversy of the day” and pointing to what the official called GAO's record of flip-flopping on past opinions.

“In their rush to insert themselves in the impeachment narrative, maybe they'll have to reverse their opinion again," the official said in a statement.