Mark Sandy, a career official at the White House Office of Management and Budget (OMB), plans to testify in connection with the House impeachment inquiry on Saturday if he is issued a subpoena.

“If Mr. Sandy is subpoenaed, he will appear for a deposition this Saturday,” Sandy’s attorney Barbara Van Gelder told The Hill on Thursday evening in an email.

Sandy would be the first OMB official to appear in the inquiry. House committees have also sought testimony from politically appointed OMB officials but none have complied with subpoenas for their appearances.

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The Washington Post was first to report that Sandy would appear if issued a subpoena.

An official working on the impeachment inquiry said Wednesday that Sandy had been scheduled to testify at a closed-door deposition on Saturday. It has been common practice by House Democrats to issue subpoenas for witness testimony, however, as with other witnesses, the issuance of a subpoena is unlikely to become public until the day of Sandy’s testimony.

As the first OMB official testifying in connection with the inquiry, Sandy could shed light on the decision by the White House to place a temporary hold on $400 million in military aid to Ukraine over the summer.

House Democrats are investigating whether President Trump Donald John TrumpFederal prosecutor speaks out, says Barr 'has brought shame' on Justice Dept. Former Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick MORE and those around him sought to use the aid as a cudgel to press Kyiv to open investigations that could help him politically. Trump asked Ukrainian President Volodymyr Zelensky to investigate 2016 election interference and the business dealings of former Vice President Joe Biden Joe BidenFormer Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick Bloomberg rolls out M ad buy to boost Biden in Florida MORE's son in Ukraine on a July 25 phone call.

A handful of witnesses have testified that OMB announced the suspension aid on July 18 but offered no reason why. Some, like William Taylor, the top U.S. diplomat in Ukraine, said the aid had been tied to a push by Trump attorney Rudy Giuliani Rudy GiulianiThe Hill's Campaign Report: GOP set to ask SCOTUS to limit mail-in voting CIA found Putin 'probably directing' campaign against Biden: report Democrats fear Russia interference could spoil bid to retake Senate MORE to get Kyiv to pursue investigations into 2016 election interference and Burisma, the Ukrainian gas company that employed Hunter Biden on its board.

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U.S. ambassador to the European Union Gordon Sondland Gordon SondlandGOP chairman vows to protect whistleblowers following Vindman retirement over 'bullying' Top Democrat slams Trump's new EU envoy: Not 'a political donor's part-time job' Trump names new EU envoy, filling post left vacant by impeachment witness Sondland MORE has also said he told a top Zelensky aid in early September that security assistance would likely not flow unless Ukraine made a public statement about launching investigations; Ukraine's foreign minister reportedly said Thursday that Sondland did not explicitly link the Biden investigation to security aid, however.

The aid was eventually released in September and Ukraine did not make a public statement about the investigations sought by Giuliani.

Trump has admitted to ordering the hold but said he did so because he was concerned European countries weren’t giving enough support to Ukraine in comparison to the United States. Trump has also denied any quid pro quo in his interactions with Ukraine.

The White House has successfully blocked a number of key officials from testifying who could shed more light on the decision, including acting chief of staff Mick Mulvaney Mick MulvaneyOn The Money: House panel pulls Powell into partisan battles | New York considers hiking taxes on the rich | Treasury: Trump's payroll tax deferral won't hurt Social Security Blockchain trade group names Mick Mulvaney to board Mick Mulvaney to start hedge fund MORE, who indicated at a press conference last month that the aid was held up in part because Trump sought an investigation by Ukraine into a debunked theory about the 2016 hack of the Democratic National Committee.

Mulvaney later walked his remarks back, saying there was no quid pro quo with respect to the investigation and blaming the media for misinterpreting his remarks.

While Sandy would be testifying in private on Saturday, House Democrats have already taken their impeachment inquiry public, receiving testimony from career State Department officials Wednesday and on Friday.