Impeachment investigators met in private on Saturday with a White House budget official, as the historic inquiry produced new testimony offering direct insight of President Donald Trump’s actions towards Ukraine.

After a week of dramatic public hearings, investigators heard late on Friday in a closed session from State Department official David Holmes, who delivered a firsthand account that puts the president at the forefront of events.

Mr Holmes, the political counsel at the US Embassy in Kiev, said he overheard Mr Trump in a phone call with his European Union ambassador, Gordon Sondland, saying he wanted Ukraine to conduct investigations.

Mr Sondland later explained the investigations pertained to “Bidens” – a reference to former vice-president Joe Biden and his son Hunter, who served on the board of a gas company in Ukraine. No wrongdoing by either Biden has been substantiated.

Trump Impeachment
David Holmes was political counsel at the US Embassy in Ukraine (Jose Luis Magana/AP)

It was one of the first direct accounts of Mr Trump seeking investigations of a political rival and provides Democrats with a counter-argument to Republicans, who dismiss the testimony so far as largely hearsay from diplomats and others with, at best, secondhand knowledge of events.

Sharpening the arguments, both sides are preparing for an intense line-up of public hearings in the coming week.

House Speaker Nancy Pelosi says the president’s actions amount to “bribery”.

In an interview to air on US network CBS on Sunday, Ms Pelosi says Mr Trump “made a mistake” by live-tweeting his criticism of Marie Yovanovitch, the US ambassador to Ukraine he dismissed, during her public testimony on Friday. Democrats said that amounted to witness intimidation.

Ms Pelosi acknowledged that presidents are able to nominate and dismiss ambassadors.

But she said Mr Trump “should not frivolously throw out insults, but that’s what he does”.

She added: “I think part of it is his own insecurity as an impostor. I think he knows full well that he’s in that office way over his head.”

Nancy Pelosi
Speaker of the House Nancy Pelosi condemned Donald Trump for ‘throwing out insults’ (J Scott Applewhite/AP)

In a speech on Friday night, Attorney General William Barr said congressional Democrats were pursuing “scores of parallel investigations through an avalanche of subpoenas” that are “designed to incapacitate the executive branch”.

Mr Barr, who favours an expansive view of executive power, said “the cost of this constant harassment is real”.

The latest witness on Saturday was Mark Sandy, a White House budget officer, as Democrats scrutinise the administration’s decision to withhold military aid from Ukraine while Mr Trump pushed the country’s new president for the political investigations.

Mr Sandy was the first official from the Office of Management and Budget to defy Mr Trump’s instructions not to testify. Like others, he received a subpoena to appear.

Questions over that trade-off – military aid and a coveted White House visit for Ukraine’s president in exchange for the investigations – are central to the impeachment inquiry.

Mr Trump insists he did nothing wrong.