(BBC) – Democrats have demanded records from the president’s personal lawyer, Rudy Giuliani, in the next step of an effort that could remove Mr Trump from office.
Mr Giuliani has admitted to asking Ukraine to investigate corruption allegations – widely debunked – against former vice-president Joe Biden.
Lawmakers issued a subpoena for those communication records from Mr Giuliani.
A phone call between President Donald Trump and the president of Ukraine was flagged by a whistleblower.
A rough transcript emerged last week of that call between Mr Trump and President Volodymyr Zelensky.
The transcript shows the US president urged him to investigate the discredited allegations against Mr Biden, a 2020 Democratic frontrunner, and his son.
The call is now at the centre of an impeachment inquiry by Democrats – an effort that could see Mr Trump expelled from office, but doing so would require members of his Republican party to turn against him.