Washington (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.

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