(CNN) An irate Donald Trump blasted Democrats for wasting Americans' time with "BULLSHIT" as his frustration with the fast widening impeachment drama that is threatening his presidency boiled over in spectacular fashion.

The President's tirade, one of the more extraordinary moments in the long history of the Oval Office, followed a warning by House Speaker Nancy Pelosi and House Intelligence Committee Chairman Adam Schiff that they were not "fooling around." They also hinted that attempts by the administration to prevent witness testimony and the handover of documents could be folded into articles of impeachment on the grounds of obstruction.

The exchanges occurred in the run-up to another crucial development in the week-old impeachment showdown, after a State Department inspector general urgently asked to brief congressional committees Wednesday on documents relevant to the Ukraine scandal.

Trump vented his feelings before the press, as the visiting President of Finland looked on.

He again accused Schiff of misrepresenting his call with the President of Ukraine, in which he is accused of asking the Kiev government to investigate his potential 2020 rival Joe Biden, in an apparent abuse of power. There is no evidence of wrongdoing by Biden.

"He should resign from office in disgrace, and frankly, they should look at him for treason," the President said, failing to outline any actual treasonous behavior by Schiff.

The comments represent an increasingly frenzied and blatant smear job of the man leading the impeachment investigation.

Trump also repeatedly misrepresented the circumstances of the call and a whistleblower's report that his administration tried to stop being released to Congress.

"The whistleblower is very inaccurate," Trump insisted, despite the fact that an intelligence community inspector general appointed by the President deemed his report "urgent and credible."

In a tweet that reflected his political strategy for fighting impeachment, Trump hit out at "Do Nothing Democrats" who he said "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, 223-306. Get a better candidate this time, you'll need it!"

The tone of Trump's comments contrasted sharply with the reserved atmosphere around an earlier news conference by Pelosi and Schiff in which they made detailed constitutional arguments as to why Trump's pressure on Ukraine met the standard of a high crimes and misdemeanor needed to consider throwing a President out of office.

The comparison revealed how each side is approaching the showdown. Democrats believe that presenting sober arguments based in constitutional law can turn the public against the President. Trump, with his warnings of coups and illegal behavior is seeking to fire up his loyal supporters to insulate him against any slippage of support among Republicans in the event of a Senate impeachment trial.

Pompeo re-ups 'bullying' claim

The State Department inspector general will be on Capitol Hill after Secretary of State Mike Pompeo admitted he was on the now-notorious July 25 call between Trump and Ukraine's President.

A congressional aide described the request by the State Department's independent watchdog official, Steve Linick, to discuss documents related to Ukraine as "highly unusual and cryptically worded."

Speaking at a news conference in Rome, Pompeo again accused Democrats of "bullying" State Department staffers, after seeking to prevent several important witnesses from appearing on Capitol Hill in the coming days. The move appeared to be an attempt to buy time to come up with a long term blueprint to save Trump by turning the politics of impeachment.

Opening another front in the investigation, Democrats on Wednesday unveiled a plan to subpoena a haul of documents from the White House pertinent to the investigation, saying they had no choice but to do so because of the administration's "flagrant disregard of multiple" requests for the material.

Pompeo's initiative was at least more substantive than Trump's tweeting and cable news appearances from conspiracy-theory touting supporters that constituted his early defense.

But the sharp Democratic response to Pompeo's claims of bullying against potential witnesses, and a key source's decision to show up anyway, suggested that the added gravity of a formal impeachment process could shift Washington's balance of power.

It is only a week since House Speaker Nancy Pelosi formally announced an impeachment probe into evidence that Trump pressured Ukraine to dig up dirt on his potential 2020 rival Joe Biden. But the drama has turned Washington on its head and comprehensively altered the dynamics of the Trump presidency.

Trump appears under siege from multiple directions. Late Tuesday, for example, The New York Times cited administration officials as saying the President previously suggested fortifying his southern border wall with a trench filled with alligators and snakes and wanted to shoot undocumented migrants in the legs.

Fast-moving developments

The latest fast-moving developments show how Democrats are using their constitutional authority to quickly build a framework for their investigation.

"This is an extraordinary crime. I suspect this is the greatest crime a president has committed in my lifetime," Rep. Mike Quigley, a Democratic member of the House Intelligence Committee told CNN's John Berman Tuesday.

The pace is sure to heat up Wednesday with Pelosi and House Intelligence Chairman Adam Schiff and the President himself expected to hold news conferences.

Trump offered Americans a glimpse into the state of his mind at the end of a tumultuous day with a unfounded tweet that warned illegal attempts were underway to steal the votes and constitutional rights of his supporters.

"As I learn more and more each day, I am coming to the conclusion that what is taking place is not an impeachment, it is a COUP," Trump declared.

Aside from the inflammatory social media posts, the White House clearly understands that its best interests lie in stalling the inquiry for as long as possible, likely with legal challenges challenging subpoenas to give its surrogates time to fog the case and to build public frustration with impeachment.

A day after being subpoenaed for documents related to his role in consultations with Ukraine, Rudy Giuliani, the President's personal lawyer, engaged his own counsel, and in an historical echo chose former Watergate prosecutor Jon Sale.

The former New York mayor has not said if he will comply with the subpoena. But he could be an early test case of the administration's intentions to gum up the impeachment works with contentious legal challenges that could last for months.

"I really have to study it. I can't shoot from the hip," Sale told CNN's Michael Warren.

"Every time I turn around, Rudy's on another TV show," Sale continued. "He and I could have a conversation, and then I turn on the television and he could be doing something else."

'Intimidation and bullying'

Pompeo, one of the President's most valued aides, launched the most serious attempt yet by the administration to disrupt the impeachment investigation on Tuesday.

In a letter to House Foreign Relations Committee Chairman Eliot Engel, he said the proposed timetable for witnesses to testify in the coming days was too compressed.

The Democratic response was swift, reflecting an apparent belief among party leaders that they have the upper hand over the administration in the early stage of the probe.

In a letter to Pompeo, who is in Europe, the chairmen of the House Intelligence, Foreign Affairs and Oversight committees said that holding back testimony "is illegal and will constitute evidence of obstruction of the impeachment inquiry."

In effect, the chairmen were warning that an attempt to frustrate the impeachment inquiry could eventually itself turn into a rationale for impeachment.

The administration has been largely successful in derailing previous Democratic efforts to oversee the White House by launching legal challenges and sweeping executive privilege claims. But impeachment already looks like a different animal.

The lawmakers also accused Pompeo of intimidating State Department witnesses to protect himself and the Ambassador Kurt Volker, the former special envoy to Ukraine who had been scheduled for a deposition on Thursday, has made clear he still plans to show up, despite Pompeo's letter.

The other officials schedules to be deposed by the House Foreign Affairs Committee include former US Ambassador to Kiev Marie "Masha" Yovanovitch, Counselor T. Ulrich Brechbuhl and Ambassador Gordon Sondland -- who were mentioned in the whistleblower complaint that helped trigger the impeachment push.

A fifth official -- Deputy Assistant Secretary George Kent -- has overseen policy on Ukraine at the State Department since September 2018 and was previously the deputy chief of mission at the US Embassy in Ukraine.

Yovanovitch, who was previously scheduled to appear Wednesday, will now do so on October 11 with the agreement of both the Committees and counsel, a congressional aide told CNN.