大象传媒

US Democrats have opened a formal impeachment inquiry into President Donald Trump over allegations he sought help from a foreign power to damage a political rival.

The most senior Democrat - Nancy Pelosi - said the president "must be held accountable".

The row was sparked by reports an intelligence whistleblower lodged a formal complaint about a phone call President Trump made with Ukrainian counterpart Volodymyr Zelensky.

While there is strong support from Democrats on impeachment, if the inquiry moves forward it is unlikely to pass the Republican-controlled Senate.

There has been talk among Democrats about impeaching Mr Trump since he took office, so why are they going ahead now and what might come of it? The 大象传媒's Washington Correspondent - Anthony Zurcher - explains.

(Photo: President Trump in the Oval Office. Credit: Getty Images)