House Democrats have begun making a strong case before Senators to remove President Donald Trump in the third ever impeachment trial in the American history. However, they ruled out a witness swap with Republicans in the trial.<br />'' <br />'' Lawmakers hope to hear testimony from Trump's former National Security Adviser John Bolton. But Democrats refused any deal to allow the son of former US Vice-President Joe Biden to be called as a witness. Trump has been touting corruption claims against Mr Biden, whose son Hunter held a lucrative board position with a Ukrainian gas firm while his father was US vice-president and in charge of American-Ukrainian relations.<br />'' <br />'' According to previous witness testimony in the House of Representatives, Democrats want to call Mr Bolton, who referred to the White House's alleged political pressure on Ukraine as a drug deal. But the former national security adviser has said he will not consider testifying unless served with a legal summons known as a subpoena.<br />'' Trump's Republican allies have argued Hunter Biden should also be ordered to appear before the impeachment trial.<br />''<br />''Trump is accused of abuse of power and obstruction of Congress. He strongly denies any wrongdoing. House Democrats have up to three days to make their case as they present their arguments in the impeachment trial in the Senate. Trump's defence team will have three days after that for a rebuttal.''<p class="MsoNormal" style="margin-bottom:0cm;margin-bottom:.0001pt;line-height:normal"><br />''</p>