The US president is accused by a mysterious whistleblower of asking his Ukrainian counterpart to investigate Joe Biden's son, his rival potential for 2020.

Donald Trump vigorously challenged accusations of a whistleblower against him on Friday, when officials are questioning pressure on his Ukrainian counterpart to press him to investigate the family of Democrat Joe Biden .

The folder, potentially explosive, still remains surrounded by many gray areas. According to the Washington Post and the New York Times the conversation with a foreign leader reported by the whistleblower concerned Ukraine. Congressional politicians are wondering about a telephone conversation in July between the US president and his Ukrainian counterpart Volodymyr Zelensky. According to the Wall Street Journal , Donald Trump, during this call, encouraged "about eight times" Volodymyr Zelensky to investigate the son of Joe Biden and to collaborate to do this with his personal lawyer Rudy Giuliani.

"It's ridiculous, it's a partial whistleblower"

Second son of the former senator, Hunter Biden worked for a Ukrainian gas group from 2014, when his father was vice president of Barack Obama. "It's ridiculous, it's a partial whistleblower," said Donald Trump from the Oval Office, while insisting he does not know his identity. "I had conversations with many leaders, they are always irreproachable," he continued, very reassembled.

Did he specifically mention Joe Biden with the Ukrainian president? "What I talked about does not matter," he said, before adding that "someone should look into Joe Biden", who could be his great rival in the presidential election 2020. The favorite of the Democratic primary rejected all suspicion surrounding the affairs of his family in Ukraine, insisting that "no credible media has [considered] credible this statement".