Democrats gave the White House a two-week deadline of Oct. 18 to comply with their demand, and they warned Mulvaney — a former House member himself — that his “failure or refusal to comply with the subpoena, including at the behest of the President or others at the White House, shall constitute evidence of obstructing the House's impeachment inquiry and may be used as an adverse inference against you and the President."

Democrats had previously warned that they would issue the subpoena for Ukraine-related documents, with Cummings even threatening the move earlier in the week if the White House didn’t provide the material by Friday.

White House press secretary Stephanie Grisham on Friday said the “subpoena changes nothing — just more document requests, wasted time, and taxpayer dollars that will ultimately show the President did nothing wrong.”

White House spokesman Judd Deere said Trump on Friday spoke with House Republican leaders, including Minority Leader Kevin McCarthy, Minority Whip Steve Scalise and Republican Conference Chairwoman Liz Cheney, and “emphasized that Speaker Pelosi and Chairman Schiff are deliberately misleading the American people about the truth, and are trampling over procedure and precedent to advance their political goals.”

Trump and other administration officials — as well as House GOP leaders — have challenged the legitimacy of the Democrats' impeachment inquiry on the grounds that the full House has not voted to begin the proceedings, as it did during previous presidential impeachment hearings.

But Schiff, Engel and Cummings insist a vote of the full House is not necessary to initiate an impeachment inquiry.

"The vote of the full House is not required to launch an impeachment inquiry, and there is no authority for the White House to make such a claim," the three chairmen asserted. "There is no such requirement in the Constitution or in House rules."

Speaker Nancy Pelosi, in an interview with the Atlanta Journal-Constitution's editorial board on Friday, wouldn't commit to holding such a vote, saying it wasn't necessary to move forward with the probe.

"If we want to do it, we'll do it. If we don't, we don't. But we're certainly not going to do it because of the president," Pelosi said.

Democrats also sent a request on Friday to Vice President Mike Pence seeking documents related to Trump’s open solicitation of assistance from Ukrainian President Volodymyr Zelensky to target Joe Biden, whose son Hunter worked for a Ukrainian energy company.

And the intelligence community’s top watchdog provided corroborating details to lawmakers about a bombshell whistleblower complaint involving Trump which has quickly become the central focus of House Democrats’ impeachment inquiry.

Michael Atkinson, the intelligence community’s inspector general, was testifying before the House Intelligence Committee when Democrats sent the request to Pence.

Democrats who emerged from the classified hearing appeared satisfied with Atkinson’s level of cooperation after more than six hours of testimony, indicating that he provided information corroborating the whistleblower’s complaint centering on Trump’s efforts to pressure Zelensky to investigate Biden.

In a statement, Schiff said the panel "explored with the IG through documents and testimony the reasons why he found the whistleblower complaint to be both urgent and credible. Now that we have all seen the call record, we can see that the IG’s determination was correct in both respects."

"[Atkinson] just cemented the integrity of how thorough he was to corroborate,” added Rep. Mike Quigley (D-Ill.), a member of the Intelligence panel. “Let’s put this in perspective, folks. What the inspector general said last time was, the whistleblower pulled the fire alarm. We have now seen the smoke and the fire.”

Quigley said Atkinson is “continuing to protect the whistleblower,” whose credibility has come under attack from Trump and his allies. Atkinson deemed the complaint “urgent” and credible after his review.

Most lawmakers were tight-lipped as they emerged from the closed-door hearing. But Rep. Jackie Speier (D-Calif.) told reporters that Atkinson spoke about the process of his investigation.

“He made a very compelling case,” Speier said.

Atkinson’s testimony came the day after a former top envoy to Ukraine provided lawmakers with damning text messages suggesting that the White House was withholding critical military assistance unless Ukraine’s president launched investigations targeting Trump’s political adversaries.

Atkinson’s appearance before the panel on Friday was his first since the whistleblower complaint was released publicly, and lawmakers were eager to hear how he handled the whistleblower's claims. It was unclear whether Atkinson would share his full report with the committee, but Democrats were insisting on it.

Atkinson returned to Capitol Hill as House Democrats ramped up their impeachment inquiry, issuing subpoenas for witness testimony and documents to better understand Trump’s efforts to solicit foreign assistance to damage Biden, a potential rival in 2020.

If the committee obtains all or parts of Atkinson’s report, Democrats’ impeachment inquiry could speed up dramatically. In the meantime, the Intelligence, Foreign Affairs and Oversight panels have been investigating Trump’s interactions with Zelensky and the extent to which State Department officials were assisting Rudy Giuliani, Trump’s personal attorney, who was in contact with Ukrainian officials regarding Biden.

The committees’ joint letter to Pence on Friday demanded documents related to Trump’s July 25 phone call with Zelensky, during which Trump pressured his Ukrainian counterpart to launch an investigation targeting Biden and his son Hunter. The request has a deadline of Oct. 15, and a subpoena could be issued if Pence doesn’t meet their demand.

The Democrats are seeking information from Pence “about any role [he] may have played in conveying or reinforcing the president’s stark message to the Ukrainian president,” the chairmen wrote.

Democrats also noted news reports that a member of Pence's staff participated in the call between Trump and Zelensky, documents Pence may have reviewed about the call, and the fact that Pence met with the Ukrainian president and reportedly discussed the administration’s hold on U.S. military assistance to Ukraine.

In response, Pence’s press secretary Katie Waldman said, “It does not appear to be a serious request but just another attempt by the 'do nothing' Democrats to call attention to their partisan impeachment.”

Friday was also the deadline for Secretary of State Mike Pompeo to comply with a Democratic subpoena for documents related to State Department officials’ involvement with Giuliani as he sought to coordinate his efforts with Ukrainian officials. And Democrats have subpoenaed documents from Giuliani and set an Oct. 15 deadline for him to turn over the material.



Pompeo did not comply with the subpoena, although Democratic aides said State Department officials had reached out to the three committees about the issue.

“Secretary Pompeo has failed to meet the deadline to produce documents required by the subpoena," said a Democratic aide. "However, the State Department has contacted the committees on this matter and we hope the department will cooperate in full promptly. Apart from the outstanding subpoena, we look forward to hearing from Ambassadors Sondland and Yovanovitch next week.”

Kurt Volker, the former U.S. special representative for Ukraine negotiations, testified behind closed doors for nearly nine hours on Thursday about his knowledge of Trump’s efforts to pressure Zelensky to investigate Biden and other political opponents. In one of the messages released by House investigators late Thursday night, Volker suggested that Zelensky’s visit to Washington is contingent on him launching an investigation into the origins of the Russia investigation, a top priority of Trump and his allies.

Trump and his allies have sought to undermine the whistleblower’s credibility by asserting that the individual did not have firsthand knowledge of Trump’s phone call with Zelensky.

However, acting Director of National Intelligence Joseph Maguire told lawmakers last week that the complaint was “in alignment” with the rough transcript of the call, and whistleblower complaints do not require firsthand knowledge of the events in question. In a statement earlier this week, Atkinson pushed back on those claims, saying the whistleblower “stated on the form that he or she possessed both first-hand and other information.”

Whistleblower protection laws require that a complaint be turned over to Congress when the inspector general deems it “urgent,” as Atkinson did in this case. But Maguire withheld the complaint from the House and Senate Intelligence committees after consulting with the Justice Department and the White House counsel’s office.

Atkinson opposed Maguire’s decision and later briefed the Intelligence Committee. But Atkinson was unable to discuss the substance of the complaint during that briefing because Maguire had not yet authorized it to be released.

In recent days, Trump and his allies have seized on the revelation that a Democratic staffer on the Intelligence Committee had brief contact with the whistleblower before he or she filed the complaint. It’s part of a larger GOP strategy to deflect criticisms from the president and instead hammer Schiff and Pelosi over how they're conducting the impeachment inquiry.

House GOP leaders are demanding a full House vote authorizing the inquiry — which Pelosi has rejected — while suggesting Schiff and his aides improperly communicated with the whistleblower before the complaint was filed.

“Chairman Schiff should be disqualified from running an investigation where his committee — members or staff — are fact witnesses about contact with the whistleblower and the whistleblower process,” Rep. John Ratcliffe (R-Texas) said after emerging from Friday's hearing in the basement of the Capitol.

But Schiff’s staff has maintained that it is normal for whistleblowers to contact the Intelligence Committee for guidance before submitting a formal complaint. A committee spokesman said earlier this week that the committee did not “review or receive the complaint in advance." The whistleblower was told to contact Atkinson's office instead, Democrats said.

Senate Intelligence Chairman Richard Burr (R-N.C.) said Atkinson’s briefing before his panel last week was “extremely helpful at trying to fill in some of the things we haven't been able to pickup from published documents.”

Daniel Lippman and Anita Kumar contributed to this report.