He also asked Linick to look into why the funds were delayed and then released, if the law was followed and any communications between the State Department, the White House and its Office of Management and Budget (OMB) about Ukraine assistance.

Trump appeared to acknowledge on Sunday that he had discussed Joe Biden on the call with Ukrainian President Volodymyr Zelensky. But he said on Monday that he did not threaten to withhold aid to Ukraine unless they investigated the Biden family.

The Washington Post reported on Monday night that Trump instructed Mulvaney to place a hold on nearly $400 million in military aid to Ukraine shortly before a phone call in which he allegedly tried to persuade Ukraine's president to investigate the Bidens.

The senior administration officials told the Post that officials within OMB passed the order on to the Defense and State departments in mid-July at an interagency meeting.

Menendez, in his letter to Mulvaney, wants to know which State Department officials were told of the decision.

He also wants a list of State Department officials briefed on the decision and any records that are in any way related to Trump's personal attorney, who has been involved in the Trump administration's politicking in Ukraine, or Ukraine assistance.