The House is holding a historic day of debate that is expected to end with votes to impeach President Trump for his conduct toward Ukraine, making him only the third president in U.S. history to receive that sanction.
At the heart of the Democrats’ case is the allegation that Trump tried to leverage a White House meeting and military aid, sought by Ukraine to combat Russian military aggression, to pressure Ukrainian President Volodymyr Zelensky to launch an investigation of former vice president Joe Biden and his son Hunter Biden, as well as a probe of an unfounded theory that Kyiv conspired with Democrats to interfere in the 2016 presidential election.
President Trump is accused of pressuring Ukraine to dig up damaging information on one of his main Democratic challengers for the presidency in 2020, Joe Biden, and his son Hunter.
Hunter worked for a Ukrainian company when Joe Biden was US vice-president.
The president is accused of dangling two things as bargaining chips to Ukraine – withholding $400m of military aid to Ukraine that had already been allocated by Congress, and a White House meeting for Ukraine’s president.
This, Democrats say, amounts to an abuse of presidential power, using the office for personal political gain and to the detriment of national security. Ukraine was using that money in its ongoing conflict with Russia.
Mr Trump is also accused of obstructing Congress by refusing to co-operate with the congressional inquiry.
A formal complaint from a whistleblower – an unnamed intelligence official who wrote a letter expressing concern about Mr Trump’s 25 July call with President Volodymyr Zelensky – kicked off the impeachment process in early September.
A rough transcript of the call revealed that Mr Trump had urged President Zelensky to investigate discredited allegations against Joe and Hunter Biden.
The call came shortly after Mr Trump had blocked the release of millions of dollars in US military aid to Ukraine. A senior official later testified that the president made clear the release of the aid was conditional on Mr Biden being investigated, but the White House denies this.
In a series of public hearings, a procession of US officials have testified that there was a White House shadow foreign policy led by the president’s personal lawyer, Rudy Giuliani.
Its aim was to get Ukraine to open an investigation into the Bidens and declare as much publicly.
The line of succession for the US government, as established by the Presidential Succession Act of 1947, would mean Vice-President Mike Pence moving into the Oval Office.