This article is more than 11 months old

This article is more than 11 months old

Donald Trump has been accused of “incitement to violence” and threatened with obstruction charges in the fast-escalating battle over impeachment, as the president maintained his aggressive counter-attack against Democratic leaders and the whistleblower who precipitated the inquiry.

Democrats issue warning over Trump’s 'dangerous' whistleblower attacks – live Read more

“We’re not fooling around here,” Adam Schiff, the chair of the powerful House intelligence committee, said in Washington on Wednesday.

Elijah Cummings, the chair of the House oversight committee, revealed that it would issue a subpoena if the White House failed to hand over documents on contacts with Ukraine by Friday.

“I do not take this step lightly,” Cummings said, saying the White House had stonewalled on demands for cooperation for several weeks.

The Democrats’ investigative steps have infuriated Trump, who was live-tweeting their press conference on Capitol Hill. He denounced the impeachment process, in block capitals, as “BULLSHIT” and later repeated an extreme claim that Schiff should be investigated for treason.

The speaker of the House, Nancy Pelosi, announced the start of the impeachment inquiry eight days ago, focusing on a whistleblower complaint that emerged the week before about a July phone call between Donald Trump and the Ukrainian president, Volodymyr Zelenskiy.

The complaint and a memo of the call issued by the White House have since been released, indicating that Trump asked Zelenskiy to investigate Joe Biden, a leading rival for the White House in the 2020 election, while the US was withholding vital aid from Ukraine.

Schiff insisted on Wednesday that the inquiry would not be slowed down by presidential “stonewalling” or threatening language against potential witnesses.

“We’re very busy,” Schiff said. “We are proceeding deliberately but at the same time we feel a real sense of urgency here.”

Democratic-run House committees heard from the state department’s inspector general, an independent watchdog, on Wednesday, followed by the former special envoy on Ukraine on Thursday and the former ambassador to Kyiv next week. But they are battling with the secretary of state, Mike Pompeo, about other depositions by state department officials and the handover of relevant documents.

Schiff and Pelosi condemned Trump for rhetoric directed at an intelligence agency whistleblower who revealed details of the phone call at the core of the impeachment proceedings.

Trump has referred to the whistleblower and the officials who provided information included in the complaint as “spies” and implied they should face the death penalty. Senior officials and some leading Republicans have confirmed the whistleblower used recommended legal channels but Trump repeated the “spy” allegation on Wednesday.

Facebook Twitter Pinterest Donald Trump at the White House with the Finnish PM on Wednesday. Pelosi and Schiff’s press conference infuriated the president. Photograph: Evan Vucci/AP

Schiff said the president was engaging in “a blatant effort to intimidate witnesses”.

“It’s an incitement of violence,” he said.

“The president probably doesn’t realize how dangerous his statement is,” Pelosi added.

Trump, who was clearly watching the press conference live, unleashed an expletive-laced Twitter tirade.

“The Do Nothing Democrats should be focused on building up our Country, not wasting everyone’s time and energy on BULLSHIT, which is what they have been doing ever since I got overwhelmingly elected in 2016,” he said.

The president continued to tweet every few minutes, lashing out at Schiff, who he called a “lowlife”, until it was time to greet the visiting Finnish president, Sauli Niinistö. The fury of Trump’s commentary reflected how impeachment has come to consume his focus and attention.

At a press conference at the end of his meeting with Niinistö, Trump, who repeated one of his favourite self-descriptions as “a very stable genius”, repeatedly refused to answer a question about what he had been asking Zelenskiy to do in relation to the Bidens, and lost his temper at the Reuters journalist asking it.

“Are you talking to me?” Trump shouted. “Did you hear me?” he demanded, telling the journalist to ask the Finnish president a question instead.

Play Video 1:25 'Are you talking to me?': furious Trump takes aim at journalist over Ukraine question – video

In his own struggle with Congress, Pompeo was forced to admit on Wednesday he took part in the July phone call between Trump and Zelenskiy.

Pompeo made the admission while on a trip to Rome, after his participation in the call had been reported in the US press. When asked in a television interview 10 days ago about the Trump conversation with Zelenskiy, Pompeo had looked quizzical and implied he was hearing about it for the first time.

On Wednesday, Pompeo said: “As for was I on the phone call? I was on the phone call.” But he presented the conversation as part of normal state department business, trying to bolster a new Ukrainian government against the threat of Russia.

He referred dismissively to the growing scandal engulfing the Trump administration as “all this noise”.

It has become clear Pompeo has only limited power to stop committees from gathering evidence for an impeachment inquiry.

One of the five witnesses deposed, Kurt Volker, former special envoy for Ukraine who resigned last week, confirmed he would speak to the committees in closed session on Thursday. The Daily Beast reported on Wednesday that Volker resigned as Pompeo was attempting to push him out of his post, in the hope of reducing the pressure on the state department.

Schiff said Marie Yovanovitch, the former ambassador to Kyiv, would appear next week. Press reports said she was due to give a deposition on 11 October.

The state department’s inspector general, Steve Linick, went to Capitol Hill on Wednesday to brief Congress on documents related to relations with Ukraine. After the briefing, the Maryland Democratic congressman Jamie Raskin described the material as a collection of unfounded allegations involving the Bidens and Yovanovitch.

“It’s essentially a packet of propaganda and disinformation spreading conspiracy theories,” Raskin said.

The president’s personal lawyer, Rudy Giuliani, who has played a central role in the Ukraine scandal, later told CNN that he had sent at least some of the material to Pompeo’s office earlier this year and that it included information he had been given by previous Ukrainian prosecutors.