WASHINGTON — House Democrats announced Wednesday that they would subpoena White House officials by the end of the week if their demands were not met for documents related to the investigation into President Donald Trump's pressure on Ukraine to investigate 2020 rival Joe Biden, as the president accused a leading congressional critic without evidence of orchestrating the whistleblower complaint at the heart of the current impeachment inquiry.

“I do not take this step lightly,” House Oversight Committee Chairman Elijah Cummings, D-Md., said in a letter to his panel notifying them that he would issue the subpoena Friday on behalf of his panel, along with the House Intelligence and Foreign Affairs committees, if the White House did not comply with the request for relevant materials. “Over the past several weeks, the Committees tried several times to obtain voluntary compliance with our requests for documents, but the White House has refused to engage with — or even respond to — the Committees."

White House officials did not directly respond to the question of whether they would comply with the subpoena, instead focusing criticism again on the impeachment process itself.

"This is nothing but more document requests, wasted time and taxpayer dollars that will ultimately show the president did nothing wrong," White House press secretary Stephanie Grisham said. "The Dems can continue with their kangaroo court, the president will continue to work on behalf of this country."

Democrats said the panels would not consider contempt or any other penalties for noncompliance, and that White House failure to produce the documents would instead be used as evidence of obstruction for impeachment.

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The impeachment inquiry officially began last week amid reports that the whistleblower's complaint involved Trump's phone call with Ukraine's leader in July.

On Wednesday afternoon, Patrick Boland, spokesman for House Intelligence Committee Chairman Adam Schiff, D-Calif., confirmed to NBC News that the whistleblower had contacted the committee for advice on how to report wrongdoing within the intelligence community ahead of the official complaint, calling it "a regular occurrence, given the Committee’s unique oversight role and responsibilities," and saying the panel's staff had "appropriately advised the whistleblower to contact an Inspector General and to seek legal counsel."

"At no point did the Committee review or receive the complaint in advance," he said.

The news was first reported by The New York Times.

Trump, asked about the development at a White House press conference, claimed without any evidence that Schiff helped the whistleblower prepare the complaint — a theory Schiff derided on Twitter soon after.

"When a whistleblower seeks guidance, staff advises them to get counsel and go to an IG," the congressman tweeted Wednesday afternoon. "That’s what they’re supposed to do. Unlike a president pressing a foreign leader to dig up dirt on a political opponent. That’s not what a president is supposed to do. And we all know it."

The latest moves came amid an escalating impeachment battle, with lawmakers rolling out a wave of planned hearings and potential subpoenas, all met with fierce resistance from White House and administration officials.

"We’re not fooling around here, though," Schiff said at a morning press conference with House Speaker Nancy Pelosi, D-Calif. "We don’t want this to drag on for months and months and months."

"We have been very busy, as you can tell, this week. We're going to be very busy against next week," he said. "We are proceeding deliberately. But at the same time, we feel there is a real sense of urgency here and that it needs to get done in a responsible period of time."

Senate Minority Leader Chuck Schumer, D-N.Y, led a rare conference call on Wednesday for Democratic senators on impeachment, according to three Democratic aides whose bosses were on the call. Schumer "outlined” a messaging strategy to put pressure on Senate Majority Leader Mitch McConnell should Impeachment pass the House.

Earlier in the day, Schiff and Pelosi spoke with reporters ahead of a closed-door Capitol Hill briefing with the State Department’s inspector general that was described as "urgent."

The Democratic leaders made clear that if the White House and the administration continue to stonewall congressional requests seeking information through testimony or documents, they will be "strengthening the case on obstruction."

"The White House needs to understand that any action like that that forces us to litigate or to consider litigation will be considered further evidence of obstruction of justice," Schiff said.

"If they are going to prevent witnesses from coming forward to testify on the allegations in the whistleblower complaint, that will create an adverse inference that those allegations are, in fact, correct."

Asked about the president wanting to interview the anonymous whistleblower, Schiff said that Democrats will "do everything in our power to make sure that whistleblower is protected, that the whistleblower’s preferences in terms of their anonymity are respected."

"This is a blatant effort to intimidate witnesses. It’s an incitement to violence," he added.

Pelosi blasted the president for "stooping to a level that is beneath the dignity of the Constitution of the United States."

"They put guardrails in the Constitution because they knew there might be someone who would overplay his or her power. They never thought that we would have a president who would kick those guardrails over and disregard the Constitution and say 'Article 2 says that I can do whatever I feel like,'" she said.

On Wednesday afternoon, the State Department’s inspector general, Steve Linick, held a bipartisan, bicameral briefing with staff from House and Senate committees that cover foreign relations, oversight issues and appropriations, which came after Linick's office reached out to the congressional committees with what they described as an “urgent request” to brief staff about documents related to the State Department and Ukraine.

Exiting the closed-door meeting that lasted a little over an hour, Rep. Jamie Raskin, D-Md., said that the State Department inspector general had handed over a packet of “disinformation” and “conspiracy theories” that had apparently been circulated, according to Raskin, as part of an effort to “sabotage” former U.S. ambassador to Ukraine Marie Yovanovitch and “to basically smear a number of employees who perhaps were getting in the way of the president.”

Raskin, who said that the packet had looked "rather amateurish" and seemed part of "an attempt to create a narrative that would somehow justify what the president did," said the origin of the material remained unknown, adding that it was possible that the packet came from the White House and that there had been misconduct by Secretary of State Mike Pompeo, but that its sourcing and initial distribution remained "the big mystery here."

The request to brief Congress came on the heels of fresh executive branch resistance to congressional investigators, with Pompeo on Tuesday portraying himself as a defender of State Department officials against Hill bullying.

“I have also been made aware that Committee staff has been sending intimidating communications to career Department professionals, who have specifically asked for Committee communications to be channeled through the Bureau of Legislative Affairs, as is customary," he wrote in a Tuesday letter to House Foreign Affairs Committee Chairman Eliot Engel, D-N.Y. "Let me be clear: I will not tolerate such tactics, and I will use all means at my disposal to prevent and expose any attempts to intimidate the dedicated professionals whom I am proud to lead and serve alongside at the Department of State.”

In the wake of Pompeo's pushback, a deposition that was expected to take place before two congressional panels Wednesday with the former U.S. ambassador to Ukraine, Marie Yovanovitch was delayed by a week.

The former U.S. envoy to Ukraine, Kurt Volker, who resigned his post last week, however, will testify before Congress on Thursday, as originally scheduled.

At Pelosi’s direction, Democrats have focused their impeachment inquiry on the whistleblower’s complaint that was made public last week regarding the phone call Trump had with his Ukrainian counterpart over the summer.

Pompeo admitted Wednesday morning — after it had been reported by multiple news outlets — that he was on that July phone call.

Meanwhile, Trump accused Democrats of launching a coup against him through their efforts to potentially impeach him.

"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," he tweeted.