The White House Office of Management and Budget made its first official move to withhold military aid to Ukraine on July 25, the same day President Donald Trump spoke to Ukrainian President Volodymyr Zelenskiy by phone, according to a summary of OMB documents produced by the House Budget Committee.

The OMB documents also show that while a career official signed that first letter to withhold the apportionment of the funds, subsequent letters to freeze the aid were signed by a political appointee, Michael Duffey, the office's associated director for national security programs. Duffey has refused to testify before House impeachment investigators despite being served with a subpoena on Oct. 25.

CNN first reported on the timing of the official hold on Ukraine aid.

The OMB documents were provided to the House Budget Committee after the panel's chairman, John Yarmuth, D-Ky., and House Appropriations Chairwoman Nita Lowey, D-N.Y., sent the administration a letter Sept. 27 seeking information about the agency's involvement in withholding of aid, including nearly $400 million in assistance for Ukraine.

The documents, which represent only a portion of the materials requested by the committee, have not been publicly released, but NBC News has reviewed a Budget Committee summary of their contents.

The committee's summary says the review of the materials made the lawmakers "more concerned that the apportionment process has been abused to undermine Congress’s constitutional power of the purse," specifically citing the timeline of the withholding of aid and the "seemingly unprecedented step" of having a political appointee handle the apportionments of funding.

OMB asserts in the documents that it first asked the Defense Department about the military aid to Ukraine on June 19, according to the summary — four weeks before the agency told an interagency group that included the Defense and State departments about the instruction to withhold all security assistance money.

The first letters signed by Duffey in the first week of August withheld two tranches of money for Ukraine, one from the State Department and then another, larger amount from the Defense Department, according to the committee's summary.

After Democrats on the House and Senate Appropriations committees wrote OMB and the White House a few days later to warn that the move could be illegal, Duffey signed another letter allowing the release of 2 percent of the State Department funds each day, but the Defense Department money continued to withheld, the summary said.

Democrats on the House and Senate Budget committees sent another letter to the administration on Aug. 19 urging the release of the aid, the summary says. Ten days after that — and one day after Politico published a story revealing the aid freeze — Duffey moved to release the State Department money at a faster rate: 25 percent each week in September. But the Defense Department aid remained on hold.

Ultimately, on Sept. 11, a few days after three House committees launched a wide-ranging investigation into the allegations that Trump, his personal lawyer Rudy Giuliani and possibly others tried to pressure the Ukrainian government to dig up dirt on Trump's political rivals, the State Department told Congress it would release the remaining Ukraine aid. The Defense Department aid was finally released on Sept. 12, the summary said.

The release of the Ukraine assistance came about a month after the first whistleblower filed a formal complaint addressed to Congress, on Aug. 12; the complaint detailed concerns over the hold on aid and the July 25 phone call, in which Trump asked his Ukrainian counterpart to investigate former Vice President Joe Biden and his son Hunter, who had business dealings in the country, as well as a debunked 2016 conspiracy theory that Ukraine interfered in the 2016 election.

The whistleblower's complaint, however, was withheld from Congress until Sept. 25, a day after House Speaker Nancy Pelosi, D-Calif., launched the impeachment inquiry based on the whistleblower complaint.