Williams testified to House investigators twice, telling them that Trump’s July 25 call with Zelensky was “inappropriate” and “political.” But after her public testimony in November, she delivered a letter to House impeachment investigators indicating she recalled new details about Pence’s Sept. 18 call with Zelensky that were relevant to the case.

Schiff asked the vice president to declassify it, claiming there was no “legitimate basis” to keep it secret. He said the decision to classify the information “cannot be justified on national security or any other legitimate grounds we can discern.”

Senate Democrats echoed that claim on Thursday. “I have no idea why they wanted to classify it,” said Sen. Debbie Stabenow (D-Mich.), emerging from the Senate’s secure facility where the letter has been made available to lawmakers.

“There is nothing I can see in that document that justifies its being classified,” said Sen. Chris Van Hollen (D-Md.).

Senate Minority Leader Chuck Schumer (D-N.Y.), too, said the information should be declassified.

Asked about the letter, Trump's longtime personal lawyer, Jay Sekulow, who is also serving as one of his trial defenders, said he wouldn’t comment on “national security” matters.

Chief Justice John Roberts, who is presiding over the trial, indicated late Wednesday “a single, one-page classified document identified by the House managers” had been entered into evidence under the Senate’s standing rules. He noted it would “not be made part of the public record.”

Rep. Zoe Lofgren (D-Calif.), one of the House impeachment managers, mentioned Williams’ supplemental testimony during her presentation to senators on Wednesday. She argued that the only reason for it to remain classified is to “cover up” the evidence.