The Trump administration complained Saturday of harassment by Democratic lawmakers who issued subpoenas for documents regarding President Donald Trump's alleged pressuring of Ukraine for political favors.

US President Donald Trump tells reporters that both Ukraine and China should investigate his potential 2020 election rival, former vice president Joe Biden
US President Donald Trump tells reporters that both Ukraine and China should investigate his potential 2020 election rival, former vice president Joe Biden AFP / Jim WATSON

And in a key development, a potential second whistleblower was reportedly weighing whether to come forward.

Former vice president Joe Biden is the leading candidate for the Democratic Party's nomination to face President Donald Trump in next year's election
Former vice president Joe Biden is the leading candidate for the Democratic Party's nomination to face President Donald Trump in next year's election AFP / Olivier Douliery

The latest explosive turns in the impeachment investigation against Trump came as Secretary of State Mike Pompeo accused Democratic-led congressional committees leading the probe of having "harassed and abused" State Department employees by contacting them directly for documents rather than going through department lawyers.

Rudy Giuliani, a personal lawyer of President Donald Trump, suggests he might not comply with a Congressional subpoena in the impeachment investigation of Trump
Rudy Giuliani, a personal lawyer of President Donald Trump, suggests he might not comply with a Congressional subpoena in the impeachment investigation of Trump AFP / Angela Weiss

"That's harassment," Pompeo said during a visit to Athens, "and I'm never going to let that happen to my team."

US President Donald Trump told reporters that both Ukraine and China should investigate his 2020 election rival, former vice president Joe Biden
US President Donald Trump told reporters that both Ukraine and China should investigate his 2020 election rival, former vice president Joe Biden AFP / Brendan Smialowski

He called the impeachment drama "some silly gotcha game," saying the matter distracts from important issues like improving lives and growing economies.

Impeachment investigation leader Adam Schiff, accused Trump of acting "with impunity" in the face of the law
Impeachment investigation leader Adam Schiff, accused Trump of acting "with impunity" in the face of the law AFP / Saul LOEB

The House committees issued their subpoenas -- including to the White House -- as evidence mounted that Trump abused his powers by attempting to withhold US military aid to pressure Ukraine President Volodymyr Zelensky into seeking damaging information on 2020 Democratic rival Joe Biden.

Trump has alleged that Biden's son Hunter earned "millions" from sitting on the board of directors of a Ukraine tycoon's gas company.

Impeachment pressure on US President Donald Trump mounted as diplomats' text messages support claims he pressured Ukraine to investigate political rival Joe Biden
Impeachment pressure on US President Donald Trump mounted as diplomats' text messages support claims he pressured Ukraine to investigate political rival Joe Biden AFP / Andrew CABALLERO-REYNOLDS

But no evidence has surfaced showing wrongdoing by either Biden.

Ukrainian President Volodymyr Zelensky (L) was allegedly pressured by President Donald Trump's emissaries to investigate political rival Joe Biden
Ukrainian President Volodymyr Zelensky (L) was allegedly pressured by President Donald Trump's emissaries to investigate political rival Joe Biden AFP / SAUL LOEB

The impeachment investigation saga began after an original whistleblower -- reportedly a CIA analyst -- filed a formal complaint to the intelligence community inspector general about Trump's alleged pressuring of Zelensky.

Republican Senator Mitt Romney said Trump's call for China and Ukraine to investigate Democratic rival Joe Biden was 'wrong and appalling'
Republican Senator Mitt Romney said Trump's call for China and Ukraine to investigate Democratic rival Joe Biden was 'wrong and appalling' AFP / DON EMMERT

"Look, nations do this," Pompeo said Saturday in Athens. "Nations work together and they say, 'Boy, goodness gracious, if you can help me with X, we'll help you achieve Y.' This is what partnerships do. It's win-win."

Michael Atkinson, the Inspector General of the Intelligence Community, arrives for a closed-door hearing before the House Intelligence Committee
Michael Atkinson, the Inspector General of the Intelligence Community, arrives for a closed-door hearing before the House Intelligence Committee AFP / Eric BARADAT

'Keep them coming!'

Trump and his supporters have aggressively attacked the still-anonymous whistleblower whom Trump has denounced as "close to a spy."

US Secretary of State Mike Pompeo, speaking in Athens on October 5, 2019, called the Democratic-led impeachment inquiry "harassment"
US Secretary of State Mike Pompeo, speaking in Athens on October 5, 2019, called the Democratic-led impeachment inquiry "harassment" POOL / COSTAS BALTAS

But if a second whistleblower emerges, and if that person has more direct information about the events in question, as The New York Times reported late Friday, the allegations would become more difficult to shrug off.

Impeachment pressure mounts on US President Donald Trump, pictured October 4, as a potential second whistleblower reportedly weighs whether to come forward
Impeachment pressure mounts on US President Donald Trump, pictured October 4, as a potential second whistleblower reportedly weighs whether to come forward AFP / ANDREW CABALLERO-REYNOLDS

However, the possibility did not seem to deter Trump, who welcomed the idea of another whistleblower, stating on Twitter: "Keep them coming!"

The Times said the second official was among those interviewed by inspector general Michael Atkinson about the allegations lodged by the original whistleblower.

Republican Senator Mitt Romney, pictured in May 2019, said Trump's call for China and Ukraine to investigate Democratic rival Joe Biden was "wrong and appalling"
Republican Senator Mitt Romney, pictured in May 2019, said Trump's call for China and Ukraine to investigate Democratic rival Joe Biden was "wrong and appalling" AFP / SAUL LOEB

The newspaper, citing two people briefed on the matter, said the second official was still pondering whether to lodge a formal complaint.

In a tweet late Saturday, Trump said that the first whistleblower "got my phone conversation almost completely wrong, so now word is they are going to the bench and another 'Whistleblower' is coming in from the Deep State, also with second hand info."

Congressional investigators led by House Intelligence Committee chairman Adam Schiff have promised a quick and expeditious inquiry, but said Friday the White House was not cooperating with their demand for documents.

"The White House has refused to engage with -- or even respond to -- multiple requests for documents," said a letter signed by the chairmen of the House oversight, intelligence and foreign affairs committees.

"His actions have left us with no choice but to issue this subpoena."

The committees ordered the White House to turn over requested files by October 18.

The subpoena followed a demand earlier Friday for documents from Vice President Mike Pence.

Pompeo -- who recently acknowledged having listened in on a key Trump-Zelensky phone call on July 25 -- failed to meet a Friday subpoena deadline to turn over Ukraine-related documents, CNN reported, citing a House foreign affairs committee aide.

Republicans quiet

Meanwhile, a series of text messages between US diplomats dealing with Ukraine, made public by the congressional investigators, supported Democratic accusations that Trump had illegally sought foreign help for his reelection effort.

The text messages showed that some US diplomats had doubts about Trump's pressure on Zelensky, including allegedly freezing a $400 million military aid package.

As Democrats raised their attacks on Trump, many Republicans remained quietly supportive of the president.

Breaking with the pack, Senator Mitt Romney, the Republican presidential nominee in 2012, blasted Trump after the US leader openly called on Thursday for Beijing and Kiev to investigate Biden. Romney called the remarks "wrong and appalling."

Senator Susan Collins on Saturday joined Romney in condemning Trump's appeal to China.

"I thought the president made a big mistake by asking China to get involved in investigating a political opponent," she told reporters in Maine, according to the Bangor Daily News. "It's completely inappropriate."