Key impeachment inquiry witnesses have said it is clear Donald Trump’s personal lawyer Rudy Giuliani was pursuing political investigations of Democrats in Ukraine at the president’s direction.

Their testimony undercuts Mr Trump’s argument that he only wanted to root out Ukrainian corruption.

State Department official David Holmes said he understood Mr Giuliani’s push to investigate “Burisma” – the Ukraine gas company where Joe Biden’s son Hunter served on the board – was code for the former vice-president and his family.

Former White House adviser Fiona Hill, meanwhile, warned investigators in her testimony that Mr Giuliani had been making “explosive” and “incendiary” claims.

David Holmes
David Holmes recalled overhearing a ‘colourful’ phone call between Donald Trump and a US ambassador (Alex Brandon/AP)

She said: “He was clearly pushing forward issues and ideas that would, you know, probably come back to haunt us and in fact… I think that’s where we are today.”

Testimony from Ms Hill and Mr Holmes capped an intense week in the historic inquiry.

The House probe focuses on allegations that Mr Trump sought investigations of Mr Biden and his son – and the discredited idea that Ukraine rather than Russia interfered in the 2016 US election – in return for military aid that Ukraine needed to fend off Russian aggression, and for a White House visit the new Ukrainian president wanted to demonstrate his backing from the West.

Ms Hill a former White House Russia analyst, sternly warned Republican politicians – and implicitly Mr Trump – to stop pushing the “fictional” Ukraine-interference narrative as they defend the president in the impeachment inquiry.

Mr Holmes testified that he came forward after overhearing Mr Trump ask about “investigations” during a “colourful” phone call with US Ambassador Gordon Sondland at a Kiev restaurant this summer.

Donald Trump
President Donald Trump has denied any wrongdoing (Evan Vucci/AP)

Mr Holmes said he heard Mr Trump ask the diplomat: “So he’s going to do the investigation?”

According to the witness, Mr Sondland replied that Ukraine President Volodymyr Zelenskiy “will, quote, ‘do anything you ask him to’”.

Mr Holmes said he realised his first-hand account of what he heard would be relevant.

“Those events potentially bore on the question of whether the president did, in fact, have knowledge that those senior officials were using the levers of our diplomatic power” to push Ukraine to investigate his rivals, he testified.

But as Mr Holmes was delivering his opening remarks, explaining how the ambassador “winced”, holding his mobile phone away from his ear because the president was talking so loudly, Mr Trump tried to undercut the career diplomat’s account of overhearing the conversation.

The president tweeted that while his own hearing is “great”, he has never been able to understand another person’s conversation that was not on speaker phone. “Try it,” he suggested.

Mr Holmes also testified about his growing concern as Mr Giuliani, the president’s personal lawyer, orchestrated Ukraine policy outside official diplomatic channels. It was a concern shared by others, he said.

The president instructed his top diplomats to work with Mr Giuliani, who was publicly pursuing investigations into Democrats, according to Mr Sondland and others who have testified this week.

Mr Holmes said he grew alarmed, watching as Mr Giuliani was “making frequent public statements pushing for Ukraine to investigate interference in the 2016 election and issues related to Burisma and the Bidens”.

The landmark House impeachment inquiry was sparked after another call, on July 25, in which Mr Trump asked Ukraine President Volodymyr Zelenskiy for “a favour” – the investigations. A still-anonymous whistleblower’s official government complaint about that call led the House to launch the current probe.

Ms Hill, who stressed she is “nonpartisan”, appealed to Republicans to stop peddling an alternative theory of the 2016 election. She contended that Russia wanted to delegitimise “our entire presidency”, whoever was elected, by sowing the “seed of doubt” in the outcome.

Fiona Hill
Former White House national security aide Fiona Hill claimed Russia is preparing to interfere in the 2020 US election (Alex Brandon/AP)

She said the current divisive American political climate “is exactly what the Russian government was hoping for”.

And she warned Russia is gearing up to intervene again in the 2020 election. “We are running out of time to stop them,” she testified.

“I would ask that you please not promote politically-driven falsehoods that so clearly advance Russian interests,” she added.

Mr Trump and Republicans on the impeachment panel continue to advance the idea that Russian interference was a “hoax” and that it was Ukraine that was trying to swing the election.

But Ms Hill said the conclusion of US intelligence agencies that Russia meddled in the last election “is beyond dispute”.

She said: “I refuse to be part of an effort to legitimise an alternative narrative that the Ukrainian government is a US adversary, and that Ukraine – not Russia – attacked us in 2016.

“I have no interest in advancing the outcome of your inquiry in any particular direction, except toward the truth.”