On Sunday, Senate Minority Leader Chuck Schumer (D-NY) zeroed in on newly disclosed emails from Mike Duffey, an Office of Management and Budget official, which show he had requested the hold on the military aid to Ukraine about 90 minutes after President Donald Trump’s infamous July 25 call with the Ukrainian president.

In the emails, obtained via FOIA request by the Center for Public Integrity on Friday, Duffey told OMB and Pentagon officials to keep information on the request “closely held to those who need to know to execute direction.”

“If there was ever an argument that we need Mr. Duffey to come testify, this is that information,” Schumer told reporters during a press conference on Sunday. “This email is explosive.”

“A top administration official, one that we’ve requested, is saying ‘Stop the aid’ 91 minutes after Trump called Zelensky, and said ‘Keep it hush-hush,'” the Democratic leader added. “What more do you need to request a witness?”

Schumer said the emails raise “at least two important questions” as the Senate prepares to hold an impeachment trial.

“First, if there’s nothing wrong with withholding the aid, why didn’t Mr. Duffey want anyone to know about what he was doing?” he asked. “If this is a perfect conversation, if this is a ok action, why are they trying to hush it up?”

“And second, from whom did Duffey get the order and why did he do it?” Schumer continued.

The New York Democrat argued that the emails further bolstered his push to allow witnesses at Trump’s Senate impeachment trial. Senate Majority Leader Mitch McConnell (R-KY), who bragged about working with White House lawyers to shield Trump from the impeachment proceedings, rejected Schumer’s request.