(CNN) -- Lawmakers return to Capitol Hill this week with House Democrats set to accelerate their impeachment inquiry against President Donald Trump.
First up: Interviews with the President's former top Russia adviser and testimony from US Ambassador to the European Union Gordon Sondland, a key witness whose earlier scheduled appearance was canceled at the last minute due to objections from the State Department.
Top Trump administration officials, including the vice president and Energy Department secretary, also face deadlines this week to turn over documents related to the Ukraine investigation, some voluntarily and some under subpoena.
Democrats face growing pressure from liberal members and activists to vote as soon as Thanksgiving, a timeline that would allow the House to avoid running into the heart of the 2020 primary season. At the same time, House Democratic leaders want to appear to be methodically collecting evidence over what they view as an abuse of power by the President in urging the Ukrainian government to investigate his potential political rival, Joe Biden, at the same time as US aid to the country had been stalled. There is no evidence of wrongdoing by Biden.
Republicans are also looking for ways to counter what many say is a partisan attack on Trump. Senate Judiciary Committee Chairman Lindsey Graham, a Republican from South Carolina, has said that he plans to invite the President's personal lawyer Rudy Giuliani to speak to his committee about Ukraine, but no date has been set for that as of now.
The timeline for the impeachment investigation is fluid and may shift depending on how events unfold, but here are key dates and deadlines in the week ahead:
Monday, October 14
- Fiona Hill, a hawk who served as Trump's top Russia adviser until she left the administration in August, is expected to be interviewed on Monday behind closed doors by three House panels as part of the Democrats' impeachment probe, according to a source familiar with the matter. Since Hill has left the administration she presumably will be free to speak her mind to the committees -- in much the way former US Special Envoy to Ukraine Kurt Volker was when he testified in early October.
- House Democrats sent a letter at the end of last month to Semyon Kislin, who they identified as a business associate of Giuliani, asking for him to appear at a deposition on October 14. There's no indication, however, that he will attend.
Tuesday, October 15
- Defense Secretary Mark Esper and acting director of Office of Management and Budget Russ Vought face a deadline on subpoenas requesting documents as part of the impeachment inquiry.
- US State Department deputy assistant secretary George Kent is expected to be interviewed, according to a schedule obtained by CNN that has been circulated among members of the three committees leading the impeachment inquiry. A "Dear Colleague" letter from House Intelligence Committee Chairman Adam Schiff on Friday stated that the committees have scheduled a deposition with Kent.
Wednesday, October 16
- Lev Parnas and Igor Fruman, associates of Giuliani face a subpoena deadline for documents. The subpoenas were issued the same day that the two were indicted by federal prosecutors. The subpoenas are separate from the indictment, in which federal prosecutors allege that Parnas and Fruman illegally funneled foreign money into US elections.
Thursday, October 17
- US Ambassador to the European Union Gordon Sondland intends to testify to the House under subpoena on Thursday, according to his lawyers. Lawmakers have been eager to press him about text messages he exchanged related to Trump's July phone call with Ukrainian President Volodymyr Zelensky and the freezing of foreign aid to Ukraine. This comes after House Democrats issued a subpoena to Sondland for him to appear for a deposition on October 16 and turn over documents by October 14. His attorneys have said that despite the subpoena for documents, they aren't able to produce any. That responsibility would fall to the State Department, they said. The Washington Post reported Saturday that Sondland is expected to tell Congress that Trump relayed to him directly in a phone call the content of a text message that Sondland sent denying quid pro quo, citing a person familiar with his testimony. Sondland is also expected to testify to Congress that he has no knowledge of whether Trump was telling him the truth at the time, according to the Post.
- US State Department counselor T. Ulrich Brechbuhl had been expected to be interviewed, according to the schedule obtained by CNN. But now that Sondland is expected to testify, it is unclear when an interview with Brechbuhl will take place. Schiff's "Dear Colleague" letter from Friday stated that Brechbuhl is one of the individuals with whom the committees have scheduled a deposition.
Friday, October 18
- Energy Secretary Rick Perry faces a subpoena deadline for documents related to the administration's dealings with Ukraine.
- House Democrats have also subpoenaed acting White House chief of staff Mick Mulvaney for documents with a deadline of October 18.