Washington: Democrats have continued their arguments for Trump's removal from office at his Senate impeachment trial, saying his conduct would put disgraced predecessor Richard Nixon to shame.

House impeachment manager Representative Zoe Lofgren was a congressional staffer during the Watergate years. Credit:AP

On Thursday (Friday Australian time) the trial turned its focus on the conduct of Joe Biden and his son Hunter, with Democrats defending the presidential frontrunner and Republicans insisting they appear to testify.

Democrats spent around an hour examining the period when Joe Biden was vice president and Hunter Biden sat on the board of controversial Ukrainian energy company Burisma.

Democratic impeachment manager Sylvia Garcia said that, rather than tackling corruption, Trump's bid for Ukraine to announce an investigation into the Bidens was driven solely by his desire for political gain.