As Republicans and Democrats continue to squabble on the terms of Trump’s impeachment trial in the Senate, newly-released government emails show that it took only about 90 minutes after Donald Trump’s infamous July telephone call to Ukrainian president Volodymyr Zelenskiy for White House officials to order the Pentagon to freeze military funding for Ukraine.

The correspondence, published by the Center for Public Integrity, appears to show that Trump appointees acted quickly after the call, behind the scenes, to block Ukrainian aid from the Pentagon.

The emails appear to confirm that the aid was held up soon after Trump pressured Zelenskiy on the call to “do us a favor, though”. That request prompted an American whistleblower who heard details about the call to complain, which in September triggered the entire impeachment inquiry.

Worried intelligence experts assessed that the president was pressing a foreign leader to investigate Trump’s US political rivals, specifically 2020 candidate Joe Biden, in return for vital military assistance for Ukraine’s armed resistance to Russian aggression on its border. Critics of the president have called that a threat to US national security and the integrity of US elections.

There were calls from prominent Democratic Senators Chuck Schumer and Amy Klobuchar this weekend for the author of the reported emails, Mike Duffey, associate director for national security programs at the Office of Budget Management, to testify in the Senate during Trump’s expected impeachment trial next year.

While House Democrats and Senate Republicans are this weekend in a standoff over terms for the next steps of the impeachment process, Klobuchar said on Sunday in CNN’s State of the Union politics news show that “I think there will be an agreement on this and the trial will go forward.”

A July email from Duffey to Pentagon officials, said: “Based on guidance I have received and in light of the administration’s plan to review assistance to Ukraine, including the Ukraine Security Assistance Initiative, please hold off on any additional DoD obligations of these funds, pending direction from that process.”

Klobuchar then read a portion of Duffey’s email out on air, while denouncing Trump’s efforts to block witnesses from testifying in the impeachment investigation so far and in the expected Senate trial, which has led to a charge of obstruction of Congress against him.

She said: “We just found out this weekend that someone who works for Mick Mulvaney, Mike Duffey, he sent an email 90 minutes after the president made the critical call to the Ukraine president … we have it here, we just found it,.”

She read out that Duffey’s email continued: “Given the sensitive nature of the request, I appreciate your keeping that information closely held to those who need to know to execute direction.”

Mulvaney is Trump’s acting chief of staff and someone whom Democrats are fiercely keen to testify to Congress. He confirmed in a White House press briefing in October that Trump had demanded a quid pro quo in his contacts with Zelenskiy, though he urged the media and critics to “get over it”.

Schumer tweeted that the email was “all the more reason why we need Duffey and others to testify in a Senate trial”.

The new documents “reveal how quickly the White House moved to cut off

military aid to Ukraine”, Susan Smith Richardson, chief executive

officer of the Center for Public Integrity, said in a statement.

On Sunday, Marc Short, chief of staff to vice-president Mike Pence told NBC’s Meet the Press that the timing of the email from Duffey was just a coincidence.

This prompted scathing comments on Twitter from legal scholar Lawrence Tribe, and George Conway, Trump critic and husband of White House counselor Kellyanne Conway.

so many coincidences https://t.co/m5BAkLdOHz — George Conway (@gtconway3d) December 22, 2019

The impeachment process is currently in limbo after articles of impeachment – effectively congressional charges against the president – were agreed last week in the House but have not yet been officially delivered to the Senate as required by protocol.

In a showdown with the Republican-controlled Senate, House speaker Nancy Pelosi, a Democrat from California, has delayed the handover of the articles saying she wants an agreement on a fair trial and the calling of witnesses.

Asked by CNN host Dana Bash on Sunday if the Senate trial could go ahead without an agreement to call witnesses, Klobuchar said she thought matters would be resolved and “the trial will go forward”.

She added: “What is shocking to me is that right now despite the president claiming innocence and saying he wants to present witnesses, he is the one blocking witnesses.”

Trump has refused to allow senior White House and administration officials, including his Mulvaney and former national security adviser John Bolton, to testify to the impeachment inquiry or cooperate with producing documents. That has led to one of the two articles of impeachment against Trump being obstruction of Congress. The other is abuse of power, over his dealings with Ukraine.

Senate majority leader Mitch McConnell has said he wants the Senate to consider the case without hearing from new witnesses.

In remarks on Sunday talk shows, Marc Short, chief of staff to Mike Pence, indicated the White House was on board with McConnell’s goal of a speedy trial.

“The American people are tired of this sham,” Short said on NBC’s Meet the Press.

After the Duffey emails were released, Rachel Semmel, a spokeswoman for the Office of Budget Management, which was included in the email chain, told the New York Times: “It’s reckless to tie the hold of funds to the phone call.”

OMB officials informed other agencies about a Ukraine aid freeze on 18 July, but the first official action to withhold Pentagon funds came on 25 July.

The timeline of events that day show Trump and Zelenskiy’s call lasted from 9.03am to 9.33am and then the email from Duffey is time-stamped 11.04am.