With Speaker Nancy Pelosi beside him, House of Representative Intelligence Committee Chairman Adam Schiff told the administration to comply with Congressional requests for documents and evidence relating to Trump's phone conversation with Ukraine's President Volodymyr Zelensky about the involvement of former Vice President Joe Biden's son Hunter in a gas company.
Schiff said, "We're not fooling around here. We don't want this to drag on months and months and months, which would be the administration's strategy."
Trump responded in a tweet, "The Do Nothing Democrats should be focused on building up our Country, not wasting everyone's time and energy on 'bull****'."
Later at an appearance with Finland's President Sauli Niinisto, Trump called Schiff a "lowlife" and dishonest guy.
The July 25 conversation between Trump and Zelensky is at the heart of the impeachment, which is the process by which the House prepares a charge sheet against the President called Articles of Impeachment and sends it to the Republican-controlled Senate for a trial and verdict.
In the call, Trump asked his counterpart to investigate Hunter Biden's role in the gas company. The company had been under investigation by a prosecutor but Ukrainian authorities had called it off.
Zelensky has said that he was not pressured by Trump, as Democrats allege.
The Democrat's case for impeachment is that Trump was pressuring a foreign leader to help him politically in the upcoming election for which the elder Biden is seeking his party's nomination and had been withholding aid to Kyiv while the call was made.
In a multi-pronged strategy, the House Oversight Committee is also seeking evidence from the White House. Its chair, Elijah Cummings, wrote to his committee that he would be issuing a subpoena to the White House and said, "I do not take this step lightly."
The whistle-blower, who made the complaint against Trump, did not hear the conversation directly but had heard about it from others.
The White House released a reconstruction of the conversation by those who heard it and not a transcript. It did not show Trump pressuring Zelensky.
Secretary of State Mike Pompeo is being dragged into the inquiry along with Rudy Giuliani, who is Trump's personal lawyer.
Pompeo was listening in on the call and is likely to be called to testify before House committees.
Giuliani had visited Ukraine to dig up information on the Bidens and had been mentioned in the Trump-Zelensky call.
A House demand for documents from Giuliani ended up as a dud on Wednesday when the State Department complied and they were found to be newspaper clippings and inconsequential notes.
Allegations of Trump trying to get help from other leaders also have surfaced, though not yet made the subject of impeachment.
Trump had reportedly asked Australian Prime Minister Scott Morrison to cooperate with Attorney General William Barr's investigations into the events leading to the probe of Russ meddling in the 2016 elections.
Morrison has dismissed the conversation with Trump as of no importance, telling Sky News, "It was a fairly polite request for something that the Australian government had made pretty clear we were happy to do."
That request related to an Australian diplomat, who reported that George Papadopoulos, a junior worker in the Trump campaign, told him in London that the Russ had damaging information on the Democratic candidate Hillary Clinton and would release them.
That tip was passed on to the Federal Bureau of Investigation (FBI), which started investigations that finally led to the setting up of a special counsel's inquiry into the allegations of Trump campaign collaboration with Russia.
The special counsel did not find any collusion between Trump and Russia.
Barr was also trying to get Italy and Britain to help with the investigations.
The Australian diplomat's role could be construed as foreign interference on the Democrat's behalf.
Democrats are also incensed by the whistle-blower's revelations that details of Trump's calls with foreign leaders are being stored in a super-secret computer with very limited access to staff.
The whistle-blower identified in media reports as a Central Intelligence Agency employee assigned to the White House complained that this was being done to protect politically sensitive material.
A likely outcome of the episode is that foreign leaders would be reluctant to speak to US leaders about highly sensitive security matters because they would fear leaks by staffers, which could tipoff adversaries of their countries or of the US.
(Arul Louis can be contacted at arul.l@.inand followed on Twitter @arulouis)
( With inputs from IANS )