Senate Minority Leader Chuck Schumer (D-NY) on Monday sent a letter to his Senate colleagues asking them to consider an "equally important aspect of the [impeachment] trial that has thus far received less attention: the need for the Senate to review documentary evidence."

"These documents fall into three evidentiary categories: (1) the effort to induce and pressure Ukraine to announce certain political investigations; (2) the withholding of a White House meeting desperately sought by the newly-elected President of Ukraine; and (3) the order to hold, and later release, $391 million in military assistance to Ukraine," he wrote.

Schumer argued that the Senate needs to have access to these documents because the White House has continually defied Congressional subpoenas. 

"As a result of this directive, the White House, Department of State, Office of Management and Budget and other agencies refused to produce a single document in response to the House's duly-issued subpoenas.  This directive not only deprived the House of relevant evidence, it will also prevent the Senate from seeing the available evidence unless the Senate takes action to obtain it," the Senate Minority Leader wrote. "By way of comparison, in the impeachment trial of President Clinton, the Senate had the benefit of thousands of pages of documents from the Department of Justice investigation by Independent Counsel Kenneth Starr."

He stated there is "no good reason" for the Senate not to have access to the documents, which he believes "will allow Senators to reach judgments informed by all of the available facts."

"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," Schumer wrote.

Specifically, Schumer wants to see:

From the White House:

From the State Department:

From the Office of Management and Budget:

According to Schumer, producing the documents wouldn't be time consuming because those agencies have already collected the documents and records as part of the House's subpoenas. 

"Production of these documents for the Senate would also ensure fundamental fairness and transparency, since the President could otherwise seek to selectively introduce documents before or during the trial in a manner that Senators could not independently evaluate as credible or reliable," he wrote. "The White House must not be permitted to selectively use documents it is withholding because the President should not be allowed to wield his obstruction of Congress as a shield and a sword."

The Senate Minority Leader argued that Trump's impeachment trial is vastly different than the Clinton impeachment trial because not all witnesses with direct knowledge have testified and not all documents have been produced.

"In this case, by contrast, the President has ordered that witnesses with direct knowledge, and documents containing directly relevant evidence, be withheld.  No good reason has been offered as to why the Senate should not hear all of the available evidence in this trial," he said. "The Majority Leader has suggested that the Senate should begin the trial and decide later whether to call witnesses or obtain documents.  The practical effect of that approach, however, would be to foreclose the possibility of obtaining such evidence because it will be too late.  Leader McConnell has made it clear that he intends to move as quickly as possible to a final vote, without any willingness to admit testimony or documents."

Schumer seems to forget that the White House invoked executive privilege. They aren't blocking Congressional subpoenas. The Democrats simply don't want to wait for a court to decide whether or not White House officials' testimonies are protected.