Senator Chuck Schumer, the minority leader, said on Monday that newly released emails showing that military aid to Ukraine was suspended 90 minutes after President Donald Trump demanded “a favour” from Ukraine’s President were “explosive”.

They strengthened, he said, Democratic demands for far more internal administration documents ahead of Trump’s impeachment trial.

The emails, made public over the weekend, included one from a White House budget office aide, Michael Duffey, telling Pentagon officials to keep quiet “given the sensitive nature of the request”.

The timing of the email — just an hour and a half after Trump raised investigations of his Democratic rivals with President Volodymyr Zelensky of Ukraine — added an element to Democrats’ contentions that they say become clearer with every new release of evidence: Trump abused the power of his office to solicit Ukraine to help him win re-election in 2020.

“What happened over the weekend has only bolstered the case that documents should be produced and witnesses testify,” Schumer of New York, the Senate Democratic leader, said at a news conference, referring to the emails released to the Center for Public Integrity.

Senator Mitch McConnell of Kentucky, the majority leader, showed no sign that he would comply with Schumer’s request. Still, Schumer clearly believed that the new emails gave Democrats momentum to present evidence in the trial that the House did not have when it charged Trump with high crimes and misdemeanours.

In a letter to his Senate colleagues, Schumer laid out a long list of records that Democrats would like to see, including internal emails and documents from the White House, the State Department and the Office of Management and Budget relating to the president’s effort to press Ukraine’s leader to investigate Trump’s political rivals.

In the House on Monday, Democrats indicated that a broader investigation into Trump was not over. The House’s counsel, Douglas

Letter, raised the prospect of a second impeachment if new evidence emerged that Trump had tried to obstruct justice. His argument was contained in an appeals court filing as part of the Democrats’ effort to press the case that they still needed the testimony of Donald F. McGahn II, the former White House counsel.

“If McGahn’s testimony produces new evidence supporting the conclusion that President Trump committed impeachable offences that are not covered by the articles approved by the House,” Letter wrote, the House Judiciary Committee “will proceed accordingly — including, if necessary, by considering whether to recommend new articles of impeachment”.

The actions in the House and the Senate may deepen the partisan impasse over Trump’s trial. If Schumer saw his document request as increasing pressure on McConnell to negotiate over the format of the proceedings, the majority leader appeared unswayed.

“Do you think Chuck Schumer is impartial?” McConnell asked during an appearance Monday morning on Fox & Friends. He went on: “So let’s quit the charade. This is a political exercise.”