MANHATTAN (CN) – Demanding that the White House stop stonewalling the upcoming impeachment trial, Senate Minority Leader Chuck Schumer pointed Monday to new revelations about the government’s delay of military aid following President Trump’s phone call with Ukrainian President Volodymyr Zelensky.

“There simply is no good reason why evidence that is directly relevant to the conduct at issue in the articles of impeachment should be withheld from the Senate and the American people,” Schumer wrote in a 4-page letter, which demands three categories of files from the White House, Department of State, and the Office of Management and Budget.

Schumer found support for his requests in a 146-page trove of files that the nonprofit Center on Public Integrity obtained pursuant to a federal court order from its Freedom of Information Act lawsuit.

Those documents included a July 25 message from President Trump’s political appointee at the Office of Management and Budget, Michael Duffey, who relayed a hold order on $391 million in military aid meant to help Ukraine in its hot war with Russia.

In a message time-stamped some 90 minutes after Trump’s call with Zelensky, Duffey wrote: “Based on guidance I have received and in light of the Administration’s plan to review assistance to Ukraine, including the Ukraine Security Assistance Initiative, please hold off on any additional DoD obligations of these funds, pending direction from that process.”

Duffey, who served as the executive director of the Republican Party of Wisconsin before Trump appointed him to his post, warned the four recipients on his email to keep the information under wraps.

“Given the sensitive nature of the request, I appreciate your keeping that information closely held to those who need to know to execute the direction,” Duffey’s letter concludes.

In a November closed-door deposition, one of the recipients of that message, the agency’s deputy associate for national security programs Mark Sandy, testified that he raised concerns about the legality of that directive.

“I just made a general reference to the Impoundment Control Act,” Sandy told lawmakers on Nov. 16, referring to legislation passed after President Richard Nixon’s impeachment meant to prevent a U.S. president from abusing his power by intruding upon Congress’ power of the purse.

The White House turned over the latest Ukraine emails in a proverbial Friday night news dump this past week, after business hours before Hanukkah and Christmas. This followed weeks of delay after U.S. District Judge Colleen Kollar-Kotelly ordered release of the records on Nov. 25. But Schumer noted that even these disclosures were pockmarked with black lines.

“The December 21st release of partially-redacted versions of these communications in response to the FOIA lawsuit further underscores why the Senate must review all of these records in unredacted form,” Schumer’s letter states.

More than a month would pass before Trump’s order withholding the aid would be publicly reported by Politico on Aug. 28, but the long delay prevented the Department of Defense from spending all of the funds appropriated by Congress by the end of the fiscal year.

For Schumer, the new documents from Duffey and others confirm what the Democrats have been saying: that the Trump administration’s blanket defiance of all congressional subpoenas stand in the way of a full and fair trial.

“The House of Representatives amassed a tremendous amount of evidence in support of the Articles of Impeachment, including extensive testimony, given in public and under oath, by senior administration officials appointed by President Trump,” his letter states. “However, the House was unable to gain access to a body of additional relevant evidence because of President Trump’s unprecedented, administration-wide directive to defy all subpoenas issued by the House, notwithstanding the fact that the House issued those subpoenas lawfully and pursuant to its constitutional impeachment power.”

Openly seeking Trump’s speedy acquittal, Senate Majority Leader Mitch McConnell and Judiciary Chairman Lindsey Graham signaled their intention weeks ago to preclude evidence-gathering at trial and to vote against Trump’s removal from office based on the House’s record.

Schumer told the Senate Republicans that this approach would amount to closing their eyes.

“To oppose the admission of this evidence would be to turn a willfully blind eye to the facts, and would clearly be at odds with the obligation of Senators to ‘do impartial justice’ according to the oath we will all take in the impeachment trial,” his letter states.

The New York Democrat had been alluding to the vow that Senate rules compel members to take as jurors during Trump’s upcoming trial next year accusing him of abusing of power and obstructing Congress: “I solemnly swear (or affirm) that in all things appertaining to the trial of President Trump, now pending, I will do impartial justice according to the Constitution and laws, so help me God.”

McConnell has claimed precedent in averting a full Senate trial in the Clinton impeachment, an analogy that Schumer called misleading. Back in 1999, Schumer noted, both political parties agreed that any new testimony would be redundant following special counsel Kenneth Starr’s investigation.

“In this case, by contrast, the president has ordered that witnesses with direct knowledge, and documents containing directly relevant evidence, be withheld,” Schumer noted. “No good reason has been offered as to why the Senate should not hear all of the available evidence in this trial.”

Duffey was among the four witnesses Schumer requested in a letter to McConnell earlier this month. The others were White House Chief of Staff Mick Mulvaney, his adviser Robert Blair, and former national security adviser John Bolton.

Now that McConnell has blocked those witnesses, Schumer asked the Senate Majority Leader to reconsider over the holiday recess.

“I urge every Senator to reflect on whether it is possible for the Senate to conduct a fair trial and reach a just outcome without reviewing all of existing evidence and considering all of the available facts,” he wrote.

By their count, Democrats need to persuade just four Republican senators to call witnesses and hear evidence to compel further fact-gathering.