Donald Trump has exploded over the ongoing impeachment inquiry in a series of tweets accusing investigators of being "human scum".
The US President deemed House intelligence committee chairman Adam Schiff "corrupt", and said his fellow Republicans were "dealing with human scum who have taken Due Process and all of the Republican Party's rights away".
There is no evidence Schiff has lied, nor that the impeachment inquiry being conducted at present is unconstitutional.
Trump's outburst followed a testimony by his Ambassador to the European Union Gordon Sondland before the House Intelligence Committee, who stated that the President did set a quid pro quo with his Ukrainian counterpart.
It also came after his former Russia adviser issued a dire warning about the country's plan to meddle in the next US election during her remarkable impeachment inquiry testimony.
Former National Security Council Director Fiona Hill today told an impeachment hearing in Capitol Hill "we are running out of time to stop" Russia from executing a plan to interfere in the 2020 presidential election.
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Hill and US Political Affairs Counselor in Ukraine David Holmes appeared before the House Intelligence Committee on Thursday in the second week of televised impeachment hearings, in which Democrats are seeking to establish whether Trump abused the power of his office by leveraging military aid and a White House meeting to extract a commitment from Zelensky to probe the Bidens.
The inquiry focuses on a July 25 phone call in which Trump is accused of asking Ukraine's new President Volodymyr Zelensky to carry out two investigations that could benefit him politically, including one targeting Democratic political rival Joe Biden and his son Hunter.
Hill warned House politicians against pushing false conspiracy theories that minimise Russia's meddling in US elections — because the Motherland is planning to do so again in 2020, according to her.
"We are running out of time to stop them," she said.
"The impact of the successful 2016 Russian campaign remains evident today. Our nation is being torn apart. Truth is questioned. Our highly professional and expert career foreign service is being undermined. US support for Ukraine — which continues to face armed Russian aggression — has been politicised.
"The Russian Government's goal is to weaken our country — to diminish America's global role and to neutralise a perceived US threat to Russian interests. President Putin and the Russian security services aim to counter US foreign policy objectives in Europe, including in Ukraine, where Moscow wishes to reassert political and economic dominance."
She also cautioned House Republicans that they should not try to involve her in backing those theories.
"And as I told this committee last month, I refuse to be part of an effort to legitimise an alternate narrative that the Ukrainian Government is a US adversary, and that Ukraine — not Russia — attacked us in 2016," she said.
"This is a fictional narrative that has been perpetrated and propagated by the Russian security services themselves."
Some Republican members of the committee have advanced an unsubstantiated conspiracy theory that Ukraine and not Russia interfered in the last presidential election, and Trump has called for Ukraine to investigate Ukraine's actions.
"The unfortunate truth is that Russia was the foreign power that systematically attacked our democratic institutions in 2016," Hill continued.
"This is the public conclusion of our intelligence agencies, confirmed in bipartisan Congressional reports. It is beyond dispute."
Devin Nunes, the ranking Republican on the committee, countered the House Republicans had already compiled an extensive report on Russian meddling — but contended that Ukraine could have meddled as well.
Nunes said it was "entirely possible for two separate nations to engage in election meddling at the same time, and Republicans believe we should take meddling seriously by all foreign countries, regardless of which campaign is the target", referring to GOP claims that Ukrainians tried to tarnish Trump to help Hillary Clinton.
In prior testimony, Hill recounted a July 10 meeting in Washington she attended with senior Ukrainian and US officials at which the investigation was discussed.
Trump, who has repeatedly denied any wrongdoing, released the aid to Ukraine on September 11.
The President this morning defended himself again over his conversations with Ukraine, saying "the calls were perfect, there was nothing said that was wrong".
"I never in my wildest dreams thought my name would in any way be associated with the ugly word, Impeachment," he wrote on Twitter.
The House investigation could conceivably wrap up this week, with evidence then sent to the House Judiciary Committee to draw up articles of impeachment.
Trump's impeachment by the Democratic-controlled House would place the President on trial in the Senate, where a Republican majority could protect him from removal.