WASHINGTON – The impeachment inquiry into President Donald Trump continued Saturday as the House Intelligence, Oversight, and Foreign Affairs Committees held a closed-door deposition with Mark Sandy, a career aide inside the White House budget office. 

Sandy, a former acting director of the Office of Management and Budget (OMB) and currently the agency’s associate director for national security programs, is the first official from OMB to testify in the impeachment inquiry. 

His testimony is likely to shed light on the Trump administration's withholding of nearly $400 million in military aid from Ukraine. 

The Democratic-led inquiry is based on a July 25 phone call between Trump and Ukrainian President Volodymyr Zelensky in which Trump discussed military assistance for Ukraine and suggested Zelensky help with investigations into Joe Biden’s son Hunter and unsubstantiated allegations about Ukraine’s involvement in the 2016 presidential election.

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Mark Sandy, a career employee in the White House Office of Management and Budget, arrives at the Capitol to testify in the House Democrats' impeachment inquiry about President Donald Trump's effort to tie military aid for Ukraine to investigations of his political opponents, in Washington, Saturday, Nov. 16, 2019.

Sandy arrives for his deposition 

Sandy has arrived for his closed-door deposition.

On Thursday, his lawyer told USA TODAY he would come testify if subpoenaed, while other White House officials have ignored subpoenas. 

“If Mr. Sandy is subpoenaed, he will appear for a deposition this Saturday,” Sandy’s attorney, Barbara “Biz” Van Gelder, told USA TODAY.

Mick Mulvaney the acting White House Chief of Staff and former head of OMB, defied his subpoena to appear before the committees on Nov. 8. 

Why is Mark Sandy's testimony important? 

Sandy could provide new evidence in the impeachment inquiry about how aid was withheld to Ukraine. 

Documents presented during the deposition of Deputy Assistant Secretary of Defense Laura Cooper showed that Sandy signed one of the "apportionment" letters in July 2019 halting security assistance to Ukraine. 

Democrats allege Trump tied the aid and a White House meeting to requests for investigations that benefited him politically.

"Based on OMB's communication with DOD on July 25, 2019, OMB understands from the Department that this brief pause in obligations will not preclude DOD's timely execution of the final policy determination," said the letter read by a congressional staff member. 

Contributing: John Fritze, USA TODAY; The Associated Press