Fiona Hill, a former White House adviser on Russia, has testified that the President of the United States of America advanced a fictional narrative about Ukraine's role in the US 2016 elections.
According to the disputed theory, it is Ukrainian nationals or individuals with Ukrainian connections who interfered in the elections.
Donald Trump, Hill told an impeachment enquiry committee, ignored the advice of senior legal experts and instead took the advice of his personal lawyer Rudi Giuliani.
The US president is being probed on whether he inappropriately pressured the Ukrainian government to undertake an investigation against former vice president Joe Biden.
Fiona Hill warned that the tendency of the president to advance fictional narratives was damaging the United States' security interests.
She said that the theories would only serve the interests of Russia.
“In the course of this investigation,” Dr Hill said.“I would ask that you please not promote politically driven falsehoods that so clearly advance Russian interests. These fictions are harmful even if they are deployed for purely domestic political purposes," she added according to the New York Times.
Donald Trump continues to disparage the impeachment inquiry as a politically motivated witch hunt and has strongly rejected suggestions that he exerted undue pressure on Ukraine.