Hours after the Senate voted against seeking new evidence in the impeachment case against Donald Trump, the administration acknowledged the existence of two dozen emails that could reveal the US president’s thinking about withholding military aid to Ukraine.

In a midnight court filing, the Justice Department explained why it should not have to unredact copies of more than 100 emails written by officials at the Office of Management and Budget and the Defence Department about the hold on funds to Ukraine.

Heather Walsh, an Office of Management and Budget (OMB) lawyer, wrote that of the 111 redacted emails in the lawsuit, 24 are protected by “presidential privilege.”

“Specifically, the documents in this category are emails that reflect communications by either the president, the vice president, or the president’s immediate advisers regarding presidential decision-making about the scope, duration, and purpose of the hold on military assistance to Ukraine,” Mr Walsh wrote.

Democrats spent much of the Senate impeachment trial imploring Grand Old Party (GOP) senators to allow new evidence in the case against Mr Trump.

All the president's lawyers: The team fighting Trump's impeachment Show all 6 1 /6 All the president's lawyers: The team fighting Trump's impeachment All the president's lawyers: The team fighting Trump's impeachment Alan Dershowitz Dershowitz is a controversial American lawyer best known for the high-profile clients he has successfully defended. Those clients have included OJ Simpson, Jeffrey Epstein and Harvey Weinstein. One longtime Harvard Law associated told the New Yorker Dershowitz "revels in taking positions that ultimately are not just controversial but pretty close to indefensible." Getty All the president's lawyers: The team fighting Trump's impeachment Ken Starr Starr became a household name in the 1990s as the independent counsel who led the investigation that led to Bill Clinton's impeachment. That investigation began as a look into a real estate scandal known as Whitewater, and eventually led to impeachment after Mr Clinton lied under oath about having an affair with White House intern Monica Lewinsky. AP All the president's lawyers: The team fighting Trump's impeachment Jay Sekulow Sekulow is the president's longtime personal attorney, and, now, personal lawyer in the White House. He has been accused by former Rudy Giuliani associate Lev Parnas of being "in the loop" during the Ukraine scandal. Getty All the president's lawyers: The team fighting Trump's impeachment Pam Bondi Bondi is the former attorney general in Florida, and a longtime backer of the president's. She made a name for herself in Florida for taking hyper partisan stances on issues, and her penchant for publicity. She is likely to be a prominent public-facing figure during the trial. AFP/Getty All the president's lawyers: The team fighting Trump's impeachment Pat Cipollone Cipollone is the White House counsel, and leading the president's defence team. Getty All the president's lawyers: The team fighting Trump's impeachment Rudy Giuliani While not officially named as one of the president's impeachment lawyers, it is hard to ignore Giuliani's outsized role in this process. The former mayor of New York has been making headlines for months as he defends his client, and for his apparent role in the effort to compel Ukraine to launch the investigation into Joe Biden. We'll see how he figures in the actual trial, which he has said he would like to be a part of. Reuters

In the weeks since the December House of Representatives vote to impeach the president, new evidence against him has emerged, including reports that former White House national security adviser John Bolton says there was a quid pro quo conditioning the aid on investigations by Ukraine that could help the president politically.

Mr Trump and administration officials repeatedly stonewalled the House impeachment probe, refusing to allow some witnesses to testify and to provide requested documents.

Ultimately Democrats could persuade only two Republicans that more evidence was needed. On Friday, the Senate voted 51 to 49 to block new witnesses and documents, clearing the way for Mr Trump’s acquittal this week.

Democrats are likely to seize on the new court filing as proof that the trial was incomplete and thus invalid.

“Every single Republican Senator voted to endorse the White House cover-up of these potentially important truth-revealing emails,” Minority Leader Chuck Schumer, Democrat for New York, said in a statement Saturday. (In fact, GOP Senators Susan Collins of Maine and Mitt Romney of Utah voted with Democrats on new witnesses and evidence.)

“Make no mistake, the full truth will eventually come out and Republicans will have to answer for why they were so determined to enable the president to hide it.”

A spokesman for Senate majority leader Mitch McConnell, Republican for Kentucky, declined to comment.

Heavily blacked-out versions of the emails in question were released in two batches in December in response to a lawsuit filed by the Centre for Public Integrity after the administration ignored a Freedom of Information Act request for the materials.

The government’s filing on Friday asked the court to deny the organisations’ request for unredacted copies.

The earliest correspondence labelled as protected presidential privilege is from 24 June, 2019, between Pentagon officials and has the subject line: “POTUS [president of the United States] follow up.”

The crux of the impeachment case against Mr Trump is whether he used the $391m (£296m) in military aid, and a coveted White House meeting for Volodymyr Zelensky, Ukraine’s president, as leverage to force the foreign leader to conduct political investigations, including one focused on former vice president Joe Biden.

In a 25 July call, Mr Trump had asked Mr Zelensky to “do us a favour.”

Why Mr Trump wanted Congress-approved assistance to Ukraine delayed is the central question of his impeachment and was a major point of tension in the Senate trial.

On Wednesday, Mitt Romney asked one of Mr Trump’s lawyers, Patrick Philbin, on what specific date Mr Trump first ordered the hold on military aid to Ukraine and what reason he gave.

Mr Philbin could not answer. “I don’t think there is evidence in the record of a specific date,” he said.

White House deputy counsel Mr Philbin answers questions in the Senate, Jan 29 (Senate Television/AP)

Referencing the 24 June email, Mr Philbin said the president had been asking since late June about how much other countries spent supporting Ukraine and had raised concerns about corruption later in the summer – the issues the White House has claimed were the impetus for the hold.

“So the evidence in the record shows that the president raised concerns, at least as of 24 June, that people were aware of the hold as of 3 July,” Mr Philbin said.

Many of the witnesses who testified in the House, some defying the White House’s orders, said they were never given an official reason for the hold.

During his 22 October, deposition, William Taylor, the acting US ambassador to Ukraine, recalled that he first learned of the hold on a 18 July conference call, when an Office of Management and Budget (OMB) aide said the security assistance was being held but could not say why.

“All that the OMB staff person said was that the directive had come from the president to the chief of staff to OMB,” Mr Taylor said. “In an instant, I realised that one of the key pillars of our strong support for Ukraine was threatened.”

Several days after that conference call, on 25 July, Mr Trump spoke to Mr Zelensky. Two hours later, a senior official at OMB, Michael Duffey, sent an email to Pentagon officials directing the hold on military aid and asking them to keep it quiet.

House Democratic managers prosecuting the case against Mr Trump argued throughout the Senate trial that there was sufficient evidence to conclude that the president was using the money as leverage to pressure the Ukrainian government to launch a public investigation into Joe Biden and his son Hunter Biden.

But White House lawyers contended that Democrats could not prove motive and suggested it was possible that Mr Trump had mixed motives in placing a hold on the aid, both personal and in the public interest.

The House managers said that was why they wanted the Senate to subpoena additional documents and witnesses with firsthand knowledge of the president’s thinking, such as acting chief of staff Mick Mulvaney and former national security adviser John Bolton.

Representative Adam Schiff, Democrat for California, who led the prosecution, warned on Friday that the contents of such emails will eventually be public.

“The facts will come out in all of their horror,” Mr Schiff said in his closing remarks. “The documents the president is hiding will come out. The witnesses the president is concealing will tell their stories. And we will be asked why we didn’t want to hear that information when we had the chance.”