The comments by Mr. Schumer of New York, the Democratic leader, came in response to an article published Sunday by The New York Times. It detailed how a number of White House advisers — including the acting chief of staff, Mick Mulvaney — dealt with Mr. Trump’s order to freeze military aid that was approved by Congress for Ukraine as it fights a war against Russia-backed separatists.

“Simply put: In our fight to have key documents and witnesses in a Senate impeachment trial, these new revelations are a game changer,” Mr. Schumer said Monday at a news conference in New York.

Mr. Schumer said Senator Mitch McConnell, Republican of Kentucky and the majority leader, must allow the Senate to get more information about the roles played by Mr. Mulvaney and a second White House aide, Robert B. Blair, in blocking the aid, as well as insight into the effort by members of Mr. Trump’s national security team in trying to get the hold lifted.