Senate Minority Leader Charles Schumer (D-N.Y.) seized on newly released emails surrounding President Trump's decision to delay aid to Ukraine, arguing they underscored the need for witnesses and documents as part of an impeachment trial.

“The newly-revealed unredacted emails are a devastating blow to Senator McConnell’s push to have a trial without the documents and witnesses we’ve requested," Schumer said in a statement.

"These emails further expose the serious concerns raised by Trump administration officials about the propriety and legality of the president’s decision to cut off aid to Ukraine to benefit himself," he added.

Schumer's comments come after Just Security obtained unredacted emails between the White House Office of Management and Budget and the Pentagon about the decision to delay aid to Ukraine.

In one email, Michael Duffey, the associate director of national security at the Office of Management and Budget, told the acting Pentagon comptroller that there was "clear direction from POTUS to hold,” according to Just Security.

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The unredacted emails are the latest round of new details on Trump's decision to delay Ukraine aid last year. The New York Times recently reported that acting White House chief of staff Mick Mulvaney and Robert Blair, assistant to the president and senior adviser to Mulvaney, were aware that the delay would prompt backlash from Congress.

Trump, according to the Times, rejected appeals to release the aid from now-former national security adviser John Bolton, Secretary of State Mike Pompeo and Defense SecretarMark Esper.

The Senate is set to return on Friday from a two-week holiday recess with negotiations over the impeachment trial at an impasse.

Democrats want the trial to include Ukraine-related documents and four witnesses: Blair, Mulvaney, Bolton and Duffey. Schumer has also specified that Democrats want one resolution, passed at the outset of the trial, that would outline both procedure and an agreement on specific witnesses.

“This new evidence also raises questions that can only be answered by having the key Trump administration officials—Mick Mulvaney, John Bolton, Michael Duffey and Robert Blair—testify under oath in a Senate trial," Schumer said Thursday.

He added that Duffey's email saying there was a "'clear direction from POTUS to continue to hold’ only further implicates President Trump and underscores the need for the Senate to subpoena the witnesses and documents we’ve requested at the onset of a trial. The American people deserve a fair trial that gets to the truth, not a rigged process that enables a cover-up.”

GOP senators have been lining up behind the idea of holding a quick trial with few, if any, witnesses.

Senate Majority Leader Mitch McConnell (R-Ky.) is pushing for the Senate to follow a framework similar to the Clinton impeachment trial in 1999, with one resolution at the start that includes the rules for the trial and a second resolution after opening arguments that would call any potential witnesses.

For Democrats to successfully call a witness they will need at least four GOP senators to clinch the 51 votes required. No Senate Republicans have specifically endorsed calling the witnesses requested by their Democratic counterparts.

Sen. Susan Collins (R-Maine), however, said she was "open" to calling witnesses but that a decision on who, if anyone, should be called should wait until after opening arguments and senators get to ask questions.