Trump, only the fourth of 45 American presidents to face the possibility of being ousted by impeachment, has to meet a 1700GMT deadline to submit his written defence.
Ukraine's investigation into whether Marie Yovanovitch was under illegal surveillance before she was recalled from her post follows the release of documents in the US showing associates of President Trump's lawyer communicating about her removal.
Bernie Sanders drew a contrast with establishment favourite Joe Biden by noting Sanders fought a 2002 measure to authorise military action against Iraq. Elizabeth Warren and Sanders locked horns over his alleged statement "a woman can't defeat Trump.
On Sunday, US President Trump wrote on Twitter that a full trial would give the Democrats undeserved credibility, and appeared instead to favour the Senate quickly dismissing the charges.
The vote, expected in the afternoon or early evening, would result in a trial next month in the US Senate in which House members would act as prosecutors.
US House Judiciary Committee voted 23-17 to approve an article of impeachment charging President Trump.
The House Judiciary Committee opens a debate session ahead of voting on articles of impeachment against President Donald Trump.
House Democrats announced articles of impeachment charging US President Trump with abuse of power and obstruction of Congress. The charges stem from Trump's pressure on Ukraine to investigate his political rivals as he blocked aid to the country.
Passage of charges against Trump in Democratic-led House, now seen as all but certain, would lead to a trial in Senate on whether to remove Trump from office. The Republicans who control the Senate have shown little sign of supporting his removal.
Legal experts gather in Washington to discuss articles of impeachment against US President Donald Trump.
Harris, 55, was the only African-American woman seeking the Democratic presidential nomination.
The House Judiciary Committee sent a two-page letter to Trump setting a deadline of 2200 GMT on December 6 for the president’s counsel to specify intended actions under the committee’s impeachment procedures.
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