Acting White House chief of staff Mick Mulvaney has snubbed the Donald Trump impeachment inquiry, skipping his deposition as Democrats wrap up closed-door interviews and move into a public phase of the investigation.

Democrats subpoenaed Mr Mulvaney late on Thursday as the White House signalled that he would not appear.

The White House instructed its officials not to comply with the investigation, which is looking at the ppresident’s dealings with Ukraine.

Mick Mulvaney
Mick Mulvaney (Evan Vucci/AP)

An official working on the inquiry said the House intelligence panel subpoenaed Mr Mulvaney because other evidence indicated he “could shed additional light on the president’s abuse of the power of his office for his personal gain”.

Mr Mulvaney said in a news conference last month that the Trump administration’s decision to hold up military aid to Ukraine was linked to Mr Trump’s demand for investigations in rival Joe Biden and his son.

He later walked back his remarks, but Democrats said that was tantamount to a confession and have cited it as evidence in their inquiry.

John Bolton
John Bolton (Carolyn Kaster/AP)

Mr Trump said on Friday that he thought Mr Mulvaney would “do great” and “I’d love to have him go up”, but he did not want to validate the investigation.

“I don’t want to give credibility to a corrupt witch hunt,” he told reporters.

The subpoena came after former national security adviser John Bolton failed to appear for an interview on Thursday. Democrats say they will use the no-shows as evidence of the president’s obstruction of Congress.

Even though some of the most high-profile witnesses have failed to appear — energy secretary Rick Perry also declined to show up this week — Democrats have indicated they think they already have ample evidence about Mr Trump’s conduct on Ukraine.

A slew of current and former officials from the State Department and White House have appeared over recent weeks and largely corroborated the same narrative — that Mr Trump delegated his lawyer Rudy Giuliani to guide US-Ukraine policy and that the two men were focused on pressuring Ukraine as the administration withheld military aid.

One Democratic member of the intelligence panel, Denny Heck, said on Thursday that there is “already a mountain of evidence” in the probe.

“I think there’s more evidence to the effect that the president shook down Ukraine, tried to cover it up, and threatened to and then withheld security assistance to Ukraine than there is evidence that the sun will come up in the east tomorrow,” he said.

Witnesses have continued to come in. On Thursday, an aide to vice president Mike Pence appeared under subpoena and was deposed for more than four hours.

Jennifer Williams, a career foreign service officer detailed to Mr Pence’s office from the State Department, was one of several White House aides who were listening in on a July phone call between Mr Trump and Ukraine President Volodymyr Zelenskiy in which the US leader asked for the investigations, according to an administration official.

Although Mr Trump has said there was no quid pro quo, several witnesses, including top Ukraine diplomat William Taylor, have testified that it was their understanding that Ukraine would not receive military assistance or a coveted Oval Office visit until it met the president’s demands.