A former White House national security official told House investigators that Gordon Sondland, ambassador to the European Union, was acting at President Trump’s behest and spoke to a top Ukrainian official about exchanging military aid for political investigations — two elements at the heart of the impeachment inquiry.

Tim Morrison, the top Russia and Europe adviser on the National Security Council, testified that between July 16 and Sept. 11, he understood that Sondland had spoken to Trump about half a dozen times, according to a transcript of his sworn Oct. 31 deposition released by House committees Saturday. Trump has said he does not know Sondland well and has tried to distance himself from the E.U. ambassador, whom Trump put in charge of Ukraine policy along with two others, even though Ukraine is not part of the European Union.

“His mandate from the president was to go make deals,” Morrison said of Sondland.

Sondland continues to emerge as possibly the key figure in House Democrats’ impeachment inquiry as multiple witnesses have now described him as central to answering the question at the heart of the effort to remove Trump from office: Did the president specifically withhold military aid and a White House visit desperately sought by the new Ukrainian government in the face of Russian aggression in exchange for investigations into his political rivals?

Sondland has provided sworn testimony behind closed doors, but questions have been raised about whether he was fully forthcoming with lawmakers. He has already revised his testimony once, and Sondland will testify publicly before the House Intelligence Committee on Wednesday in what is now a highly anticipated appearance.

The release of Morrison’s transcript came as a longtime budget official gave sworn testimony behind closed doors Saturday that the White House decision to freeze military aid to Ukraine in mid-July was highly irregular and senior political appointees in the Office of Management and Budget were unable to provide an explanation for the delay.

The testimony from Mark Sandy, the first employee of OMB to testify in the House impeachment probe, appeared to confirm Democrats’ contention that the decision to withhold nearly $400 million in congressionally approved funds for Ukraine, including millions in lethal aid, was a political one.

Sandy, the deputy associate director for national security programs at OMB, testified that he was instructed to sign the first of several apportionment letters in which budget officials formally instituted the freeze on funds, according to two people familiar with his testimony who spoke on the condition of anonymity to speak frankly. He was never given a specific reason as to why the letter was being sent out, the people added.

Other witnesses have testified that the letter Sandy signed was dated July 25 — the same day that Trump spoke by phone with Ukrainian President Volodymyr Zelensky, and one week after OMB verbally informed interagency officials that they were withholding the funds on orders from the White House. The signature of Sandy’s boss, political appointee Michael Duffey, appears on subsequent letters.

Sandy testified that the change came about when Duffey told him he wanted to learn more about the budget apportionment process. Sandy thought this was odd, the people familiar with his testimony said — and told investigators that he suggested to Duffey that if he wanted to learn more about the process, there were other ways to do it. But Duffey insisted.

Sandy testified that he had never in his career seen a senior political OMB official assume control of a portfolio in such a fashion, according to the people familiar with his testimony.

In the transcript of his closed-door deposition released Saturday, Morrison outlined Sondland’s actions and statements — raising the stakes for the E.U. ambassador’s public testimony Wednesday.

He said he spoke to Sondland after the ambassador had a conversation with Andriy Yermak, a top aide to Zelensky, following a meeting between Zelensky and Vice President Pence in Warsaw in early September. That conversation was part of an amendment that Sondland made to his testimony, in which he said that he told the Ukrainian official that if his country did not announce the investigations Trump wanted — probes into former vice president Joe Biden and his son Hunter, as well as an unfounded theory of Ukrainian interference in the 2016 election — military assistance might not flow.

According to Morrison, who spoke to Sondland directly after his conversation with Yermak, Sondland “told me that in his — that what he communicated was that he believed the — what could help them move the aid was if the prosecutor general would go to the mic and announce that he was opening the Burisma investigation.”

Hunter Biden had served on the board of Burisma while his father was the point man on Ukraine policy for the Obama administration.

Morrison later clarified that by Burisma he meant investigations generally, but he said that in his conversation with Sondland, the word Burisma did not come up, nor did the names Joe or Hunter Biden.

But Sondland’s conversation with Yermak appeared to have struck Morrison as concerning. He spoke to then-national security adviser John Bolton, whose direction “consistent with my instinct, was make sure the lawyers are tracking.”

Morrison said that at other times he spoke to Sondland about his activities, which took place outside normal channels. “I would offer him counsel on what others in the interagency were doing that he should factor into his instinct or his impulse, or I would tell him that I thought there was perhaps a more effective way to get it done than he was contemplating.”

Morrison said Fiona Hill, the NSC official he replaced, advised him to “steer clear of Gordon.

“And I said I thought what would be more effective and the approach I would pursue was I’d rather have him inside the tent, you know, rather than outside the tent. And so I wanted to know what he was doing and do my best to spy, you know, problems as opposed to being ignorant,” Morrison testified.

Morrison, however, left open the question of whether Sondland was acting directly on orders from the president or was taking his own initiatives based on what he thought Trump wanted.

He recalled talking to Kurt Volker, the former envoy to Ukraine, after an Aug. 2 White House meeting and pressing him on Sondland and the president’s personal attorney, Rudolph W. Giuliani, who was publicly discussing his desire for Ukraine to launch political investigations into Trump’s rivals. “I think we both agreed that Ambassador Sondland was, you know, sort of a free radical. He was sort of out there, engaging when he wanted, and it was not always possible to keep track of what it is that he was doing and who he was talking to.”

At the same time, Morrison said he reported interactions with Sondland up the chain of command, including to attorneys and Bolton, to “protect the president.”

“Ambassador Bolton is fond of saying that the process is your protection. So part of what I’m trying to do here in talking to the lawyers is making sure they’re aware of what Mr. Sondland is doing. And he’s saying the president is aware, but I’m still not entirely certain that he is,” Morrison testified.

Democrats couldn’t get Morrison to pin anything on Trump directly. He qualified several times that his understanding of Trump’s involvement came from Sondland.

Morrison also told lawmakers that he feared leaks of the contents of the July 25 call between Trump and Zelensky where Trump brought up Bidens and the theory about the 2016 election would be damaging, so he recommended restricting access to the transcript.

Morrison, who left the job at the end of October, said he knew immediately after listening to the call that they needed to keep it under wraps.

“I recommended to them that we restrict access to the package,” Morrison said.

He said it was the only time he had ever asked the NSC legal team to restrict access.

He said his concern was how the rough transcript would “play out in Washington’s polarized environment” and affect Ukraine’s view of its relationship with the United States. He said he “grew concerned that the call was not the full-throated endorsement of the Ukraine reform agenda that I was hoping to hear.”

But Morrison said it was a “mistake” that the call transcript ended up transferred to a highly classified system reserved for code-word intelligence rather than the normal “Portal” system that has restricted access.

And even though he feared the conversation leaking, Morrison broke with colleagues in telling House investigators that he heard nothing “improper” on Trump’s call with Zelensky.

Morrison’s interpretation of the controversial call, which sparked the impeachment proceedings, could also make him a valuable witness for Republicans, who complained on Friday that Democrats were delaying the release of his testimony.

“In your view there was nothing improper that occurred during the call?” the Republican’s lead counsel asked Morrison.

“Correct,” he replied.

Morrison expressed frustration that Lt. Col. Alexander Vindman, one of his subordinates who will testify publicly next week, had gone to the NSC’s top lawyer with concerns about the call in which Trump pressed Zelensky to investigate the Bidens.

He also disputed Vindman’s account in which he asked for edits to the document to include a mention of Burisma, the gas company that employed Hunter Biden on its board.

“I believe it was accurate and complete,” Morrison said of the rough transcript. He said he recalled accepting all of Vindman’s proposed changes. Morrison’s recollection, though, contradicts the notes of Jennifer Williams, a top aide to Pence, who said Burisma was mentioned on the call. Williams’s transcript was also made public Saturday.

Williams’s contemporaneous notes of the July 25 call reflected that Zelensky referenced Burisma during the call, her lawyer stated in a Nov. 11 release with her deposition transcript, in contrast with the transcript summary of the call released by the White House.

Williams testified that the call was “unusual” given the mention of specific investigations

“I guess for me it shed some light on possible other motivations behind a security assistance hold,” she said.

“The testimony released today shows that President Trump’s July 25 phone call with Ukrainian President Zelensky immediately set off alarm bells throughout the White House,” said Intelligence Chairman Adam B. Schiff (D-Calif.), Foreign Affairs Chairman Eliot L. Engel (D-N.Y.) and acting Oversight Chairwoman Carolyn B. Maloney (D-N.Y.) in a joint statement.

Williams also testified that Pence’s canceled trip to attend Zelensky’s inauguration was decided by Trump. She said she was never given an explanation for the change in plans.

“My understanding from my colleague — and, again, I wasn’t there for the conversation — was that the President asked the Vice President not to attend,” she told lawmakers.

CORRECTION: An earlier version of this story said Mark Sandy, a career OMB official, did not object to a political appointee taking over decision-making on aid to Ukraine because he wanted to keep his job, according to two people familiar with his closed-door deposition Saturday. Sandy’s lawyer, Barbara Van Gelder, said in a statement Sunday that her client did not express fear about losing his job. This article has been updated to reflect that.

Elise Viebeck and Mike DeBonis contributed to this report.