Fiona Hill, a former special assistant to US President Donald Trump on Russian affairs, is the latest figure to testify to Congress in the burgeoning impeachment investigation (Alex Wroblewski)

Washington (AFP) – US lawmakers returning from a two-week break braced for an impeachment brawl in Washington, as a former White House aide testified before Congress Monday in the latest twist in the investigation of President Donald Trump.

Republicans already at odds with Trump over his withdrawal of US troops from northern Syria face questions about the embattled president’s efforts to pressure his Ukrainian counterpart to investigate his Democratic rivals.

Congress returns to work Tuesday with what Republican Senator Chuck Grassley called an “impeachment cloud” over Washington.

Trump has pushed back, with no fewer than 10 tweets Monday against Democrats and their investigation.

In one he demanded that a whistleblower whose warning about the US president’s call with Ukraine triggered the impeachment inquiry be identified and testify before Congress.

As he menaced the person who exposed his possible wrongdoing, Trump faced a potential setback with his former top Russia advisor, Fiona Hill, sitting for an hours-long closed-door deposition before US lawmakers.

Hill served in the National Security Council but left the administration shortly before Trump’s July 25 call with his Ukrainian counterpart Volodymyr Zelensky.

Democrats expect her to share her concerns about Trump’s involvement in the Ukraine scandal, including his ouster of the US ambassador to Kiev Marie Yovanovitch, who testified to Congress last week.

With the impeachment inquiry charging ahead, Trump’s re-election team launched a fierce broadside at the investigators.

“Democrats have crossed over the line of partisan politics and have undertaken a seditious conspiracy to overthrow the people’s president,” Trump’s 2020 campaign manager Brad Parscale said.

Trump himself lashed out at House Intelligence Committee chairman Adam Schiff after the Democrat suggested the whistleblower may not testify out of safety concerns.

Trump has repeatedly pushed for the unmasking of the author of a complaint that said the president may have abused his power on the call by urging Ukraine to dig up dirt on his political rival Joe Biden.

Whistleblowers are protected by US law, and revealing their identity is a crime.

“Adam Schiff now doesn’t seem to want the Whistleblower to testify. NO! Must testify to explain why he got my Ukraine conversation sooo wrong,” Trump tweeted.

“We must determine the Whistleblower’s identity to determine WHY this was done to the USA.”

The White House’s call memo shows Trump sought a “favor” from Zelensky. Democrats say it was a demand to investigate Biden — the president’s potential 2020 election rival — and a Ukrainian firm that hired Biden’s son Hunter.

– ‘Premeditated strategy’ –

Hill meanwhile appeared before congressional investigators despite the White House declaration last week that it would not cooperate with the probe.

Her lawyer Lee Wolosky said Hill had “received a congressional subpoena” to testify, suggesting top Democrats had feared the White House might seek an 11th-hour block to her testimony, as they did with previous witnesses.

House Democrat Jamie Raskin said he believes Hill could shed light on what he described as “a very powerful shadow foreign policy being operated out of Ukraine by the president’s lawyer Rudy Giuliani” that bypassed normal channels in order to apply coercive pressure on Kiev.

“I think that she would have a comprehensive overview of that whole situation,” Raskin told MSNBC.

Raskin said testimony from various witnesses also appears to confirm a “deliberate, premeditated strategy by the president” to condition some $390 million in military assistance to Ukraine on that country investigating the Bidens.

Testifying on Thursday will be US Ambassador to the European Union Gordon Sondland, who shortly before Trump’s Ukraine call participated in several text messages with other US diplomats who expressed concern that Trump was seeking a quid pro quo for the military aid.

According to the Washington Post, Sondland intends to tell Congress that his text to a fellow diplomat denying such a trade-off was relayed directly to him by Trump.

Disclaimer: Validity of the above story is for 7 Days from original date of publishing. Source: AFP.