A member of US President Donald Trump's defence team said that impeachment was "hell" and "tantamount to domestic war," as the impeachment trial continued in the US Senate in Washington DC on Monday.

"Like war, impeachment is hell," lawyer Kenneth Starr told senators. "It's filled with acrimony and divides the country like nothing else. Those of us who lived through the Clinton impeachment understand that in a deep and personal way."

Starr was a central figure in the investigation that led to former President Bill Clinton's impeachment trial in 1998.

On Monday revelations emerged from a draft for an upcoming book by former US National Security Advisor John Bolton, who alleges that Trump stated he was withholding military aid from Ukraine in exchange for political favours.

The Bolton allegations have led Senate Democrats to urge Republicans to join them in voting for him to be called as a witness in the ongoing impeachment trial.

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