In an early test of the former president's defence, Mr Trump's team lost a crucial bid to halt the trial on constitutional grounds. Senators confirmed, 56-44, their jurisdiction over the trial, the first of a president no longer in office.
While six Republican senators joined the Democrats in proceeding, the tally showed how far prosecutors have to go to win conviction, which requires a two-thirds threshold of 67 senators.
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House impeachment manager Rep. Jamie Raskin is leading the second trial of former president Donald Trump in the US Senate.(AP)
A chart displayed during Mr Raskin's opening remarks to support Democrats' claims the trial is constitutionally sound.(AP)