In return for those investigations, Democrats say Mr Trump offered two bargaining chips – $ (m) £ 90 m) of military aid that had already been allocated by Congress, and a White House meeting for President Volodymyr Zelensky.
Democrats say this pressure on a vulnerable US ally constitutes an abuse of power.
The first investigation Mr Trump wanted from Ukraine was into former Vice-President Joe Biden, his main Democratic challenger, and his son Hunter. Hunter Biden joined the board of a Ukrainian energy company when his father was President Barack Obama’s deputy.
The second Trump demand was that Ukraine should try to corroborate a conspiracy theory that Ukraine , not Russia, had interfered in the last US presidential election. This theory has been widely debunked, and US intelligence agencies are unanimous in saying Moscow was behind the hacking of Democratic Party emails in 2016
How strong is the case for impeachment?
President Trump railed at the announcement of the charges, declaring again on Twitter that it was a “witch hunt”.
“Nadler just said that I ‘pressured Ukraine to interfere in our 50731010 Election ‘, “he wrote.
” Ridiculous, and he knows that is not true. Both the President & Foreign Minister of Ukraine said, many times, that there is “WAS NO PRESSURE.” Nadler and the Dems know this, but refuse to acknowledge! “
Law professor, Jonathan Turley, who testified for Mr Trump’s Republican Party before the House Judiciary Committee, told the BBC: “The problem is not with the legal basis for such impeachable offenses but the evidentiary record.
“This record remains both incomplete and conflicted. The Democrats have insisted on impeaching by Christmas rather than build a record to support such charges. This is now the fastest investigation with the thinnest record supporting the narrowest impeachment in modern history. “
How does impeachment work?
Impeachment is the first part – the charges – of a two-stage political process by which Congress can remove a president from office.
If the House of Representatives votes to pass articles of impeachment, the Senate is forced to hold a trial.
A Senate vote requires a two-thirds majority to convict and remove the president – unlikely in this case, given that Mr Trump’s party controls the chamber.
Only two US presidents in history – Bill Clinton and Andrew Johnson – have been impeached, but neither was convicted.
President Richard Nixon resigned before he could be impeached.