In July, US President Donald Trump called his Ukrainian counterpart, Volodymyr Zelenskiy.

According to a complaint made by a US intelligence official, during the call, Trump urged Zelenskiy to investigate Joe Biden’s son, Hunter, a former director of a Ukrainian business.

The implication was that Trump was seeking a foreign country's aid in damaging a domestic political rival.

Last Thursday, the Democrats in Congress heard the White House had blocked them from hearing the details of the complaint lodged with the inspector general about the incident.