(CNN) House Intelligence Committee Chairman Adam Schiff is moving quickly to investigate allegations at the center of the impeachment inquiry into President Donald Trump, preparing for hearings, subpoenas and depositions as soon as next week as Democrats try to finish the probe this fall.

The panel is in negotiations to interview the whistleblower who wrote in August an extraordinary complaint to intelligence community inspector general Michael Atkinson alleging that Trump asked Ukraine's President to initiate an investigation that could have benefited his reelection. Senior White House officials then endeavored to conceal records of the call including the official transcript, according to the complaint.

Schiff told CNN on Friday the committee expects a hearing as soon as next week, while the rest of Congress will be back in their districts for a two-week recess. The panel will hold another closed briefing with Atkinson on October 4, according to a source on the House Intelligence committee.

"We will move as expeditiously as possible," said Schiff. "But we have to see what witnesses are going to make themselves available and what witnesses are going to require compulsion."

If the White House stonewalls the investigation, he added, "It'll just strengthen the case on obstruction," an impeachable offense. The panel and House Oversight consulted with the House Foreign Affairs committee to subpoena Secretary of State Mike Pompeo on Friday over his failure to produce documents related to Ukraine.

Once it has exhausted its options — either by getting information or if the White House blocks its investigation — Democrats may move forward with articles of impeachment, potentially over obstruction of justice, obstruction of Congress and abuse of power.

It is unclear whether Schiff will invite other witnesses to come before his panel, but Democratic lawmakers on it would like to hear from people mentioned in the whistleblower's complaint, including Rudy Giuliani, Trump's personal attorney, and Attorney General Bill Barr.

"The discussions are underway between the relevant parties representing the whistleblower and others to see if that's an opportunity that can be afforded to us," Rep. Denny Heck, Democrat of Washington, told CNN. "My view is the sooner the better. I would hope that that would happen within the next two weeks."

"I would like next to talk to the whistleblower," he added.

House Democrats are hoping for a speedy process, aiming to potentially move forward with impeachment by Thanksgiving. While the Intelligence Committee continues its investigation over the October recess, the House Judiciary Committee is likely to begin sifting through existing evidence and considering a path forward for articles of impeachment, members say.

"I think members of the Judiciary Committee are going to be conferring with each other and thinking about some of the legal frameworks and some of the evidence that we've collected already, and what that supports in terms of articles of impeachment that we may or may not recommend to the full House," Rep. David Cicilline told CNN on Friday.

It remains a key unanswered question what articles of impeachment could look like — it depends on the Intelligence Committee's ongoing investigation -- but Democrats are largely agreed on the focus for now. The Ukraine matter, Cicilline said, "has to be the centerpiece of any impeachment proceedings."

House Intelligence Committee Chairman Adam Schiff, a California Democrat, speaks at the Capitol in Washington earlier this week.

On a July 25 phone call, Trump pressed Ukrainian President Volodymyr Zelensky to investigate Biden's son Hunter, who sat on the board of an energy company, Burisma Holdings, whose owner was investigated by Ukrainian general prosecutor Viktor Shokin. There is no evidence of wrongdoing by either Joe or Hunter Biden.

"There's a lot of talk about Biden's son, that Biden stopped the prosecution and a lot of people want to find out about that so whatever you can do with the attorney general would be great," said Trump on the call, according to a reconstructed transcript released by the White House. "Biden went around bragging that he stopped the prosecution so if you can look into it ... It sounds horrible to me."

Trump also said he wanted his personal lawyer, Rudy Giuliani, and Attorney General Bill Barr to call Zelensky.

On August 12, a whistleblower expressed concerns to the intelligence community's inspector general Michael Atkinson about Trump's call with Zelensky. Atkinson deemed them credible and urgent and sent the complaint to acting Director of National Intelligence Joseph Maguire. The complaint was released ahead of Maguire's testimony Thursday before the House Intelligence Committee. Trump has denied any wrongdoing.

Reps. Eric Swalwell and Jackie Speier, California Democrats on the Intelligence committee, told CNN they have canceled events in their districts next week to prepare for potential action on the panel.

Speier told CNN she had a number of questions for the whistleblower, including whether he or she has additional information regarding other phone calls or circumstances "in which there's been a quid pro quo kind of environment."

"I want to know who else was privy to this information and didn't speak up," Speier said. "We all take an oath of office when we become federal officials, and many of those people in the White House are federal officials."

"There were gross violations of law and yet, he or she is the only person who came forward," she added.

Rep. Raja Krishnamoorthi, Democrat of Illinois, said both Giuliani and Barr are "obviously central figures" in the complaint but that he would defer to Schiff on whether to invite them before the committee.

"I'm not too worried that, if we call Rudy Giuliani for a hearing that he wouldn't show up," added Krishnamoorthi.

This story has been updated with additional developments Friday.