Donald Trump’s defence attacked Joe Biden and his son Hunter on Monday to try to demonstrate that the American president was within his rights by asking Ukraine to investigate them, a request in the center of his impeachment trial in the Senate.

Trump is accused of conditioning crucial military aid on Kiev’s investigation into Democrat Joe Biden, his potential opponent in the November presidential election, and his son. Hunter Biden sat between 2014 and 2019 on the board of directors of the gas company Burisma, a time subject to investigations for corruption.

Trump’s defence suggested on Monday that the former US vice president, who was then overseeing Washington’s policy on Kiev, had asked for and obtained the head of the Ukrainian attorney general to protect his son’s employer.

Hunter Biden was hired by Burisma when he had “neither expertise nor experience” in the gas industry or Ukrainian law, said Eric Herschmann, one of the president’s lawyers.

“Why did Burisma want Hunter Biden on its board of directors?” He was the son of the man in charge of Ukraine, ”said Herschmann.

Pam Bondi, another member of Trump’s team, also pointed out that “all the witnesses” heard during the impeachment investigation “agreed on the possible appearance of a conflict of interest” regarding Hunter Biden’s presence in the company when his father was vice-president.

She said the charge file “crumbles” as soon as it is accepted that Mr. Trump’s concerns are legitimate.