WASHINGTON — Two officials at the White House budget office resigned this year partly because of their concerns about President Trump’s decision to hold up congressionally approved security assistance to Ukraine, a third aide at the office told impeachment investigators, revealing dissent within a key agency about Mr. Trump’s refusal to release the money.
Mark Sandy, an official at the White House Office of Management and Budget, told the House Intelligence Committee in a private interview this month that one of the officials “expressed some frustrations about not understanding the reason for the hold” before resigning in September.
A second co-worker, an official in the legal division of the office, also resigned after offering a “dissenting opinion” about whether it was legal to hold up the aid, Mr. Sandy testified, according to a transcript of his testimony released by the committee on Tuesday.
He did not identify either official, and it was unclear how senior they were or how directly their resignations were tied to their concerns over the withholding of the aid. But Mr. Sandy’s account of their departures — after weeks of unanswered questions inside the budget office about why Mr. Trump had directed the funding frozen — underscores the depth of the pushback inside a key White House agency about a decision many officials believed was legally questionable and potentially dangerous.
The issue is at the core of the impeachment inquiry, which marched forward on Tuesday as the House Judiciary Committee announced its first hearing next week and invited Mr. Trump’s legal team to participate. Democrats have charged that Mr. Trump abused his power to enlist Ukraine in smearing his political rivals, in part by withholding the nearly $400 million package of aid the country desperately needed while insisting that its leaders announce investigations of former Vice President Joseph R. Biden Jr. and other Democrats.
Mr. Trump has insisted he never pressured Ukraine for the investigations or made the aid contingent upon them, and was instead withholding the money out of concern for corruption in Ukraine and a desire to have other countries pay their fair share. And his Republican allies have argued that the funding’s eventual release proves that Mr. Trump did nothing wrong.
But the money was delivered only after a bipartisan outcry by lawmakers and after the White House became aware of a whistle-blower complaint that alleged Mr. Trump was using the funding as leverage. Two people familiar with the matter said on Tuesday that Mr. Trump had been briefed on that complaint when he unfroze military aid for the country in September.
Several diplomats and national security officials have testified that the freeze generated discord at the State Department, the Defense Department and the National Security Council, where top officials were worried about the security implications for Ukraine, as well as the legal implications of denying money allocated by Congress.
Mr. Sandy testified that he was informed that the aid freeze came directly from Mr. Trump, who he was told began inquiring about the assistance package on June 19, after seeing a news media report. Mr. Sandy learned of Mr. Trump’s decision to put a hold on the aid through a July 12 email from Robert Blair, a top aide to Mick Mulvaney, the acting White House chief of staff.
That email, which Mr. Sandy received nearly a week before other administration officials have said they learned that the aid had been frozen, indicated that “the president is directing a hold on military support funding for Ukraine,” he told impeachment investigators.
In an indication of the level of frustration about the situation inside the budget office, Mr. Sandy said he and others repeatedly asked his superiors why the security assistance had been frozen, but were never given a rationale.
“It was an open question over the course of late July and pretty much all of August, as I recall,” Mr. Sandy said.
He equivocated when asked whether both his former colleagues resigned because of their concerns about the aid, making it clear that he drew the conclusion himself. “I’m always reluctant to speak to someone else’s motivations,” he cautioned.
“I never want to attribute that as the, you know, sole purpose for an individual’s actions, but I am aware of their frustrations in that area, yes,” he said of the official in the legal office.
Mr. Sandy is the only official at the budget office to testify in the impeachment inquiry. Several others, including Russell T. Vought, the acting head of the office, have refused to appear.
The House Intelligence Committee released the transcript of his Nov. 16 testimony, along with one of an interview by Philip T. Reeker, the acting assistant secretary of state in charge of European and Eurasian affairs, as Democrats were pushing forward with the next phase of their impeachment inquiry.
Also on Tuesday, the Judiciary Committee announced it would convene its first hearing in the matter on Dec. 4, calling a panel of constitutional scholars to inform the debate over whether to impeach Mr. Trump.
The hearing is similar to one the panel held in 1998, when it began debate over whether to impeach President Bill Clinton.
Representative Jerrold Nadler, Democrat of New York and the Judiciary Committee chairman, wrote a letter to the president Tuesday afternoon notifying him of the hearing and offering his lawyers a chance to question the witnesses. He asked the White House to inform him by Sunday if the president or his lawyer wants to participate in the initial hearing, and reminded Mr. Trump that House rules empower him as chairman to curtail that involvement if “you continue to refuse to make witnesses and documents available” related to the inquiry.
The White House did not immediately respond to the letter or a request for comment. Mr. Trump’s allies have complained bitterly for weeks that the president’s legal team did not have a seat at the table during the Intelligence Committee’s investigation into his actions involving Ukraine, but they have also sought to avoid any move that could be seen as giving the inquiry legitimacy.
The first Judiciary Committee hearing will probably take place just as the intelligence panel sends its written report summarizing the findings of its two-month investigation. In the coming days, Democrats could schedule another hearing for the Intelligence Committee to formally present its work to the judiciary panel.
But information related to the investigation continued to trickle out. On Tuesday, Democrats on the House Budget Committee released a summary of documents from the White House budget office that asserted that administration officials improperly held up the funds for Ukraine. The summary said a decision by Michael Duffey, a political appointee in the office, to take authority over the funds was “a troubling deviation” from procedures.
The transcript of Mr. Reeker, the State Department official, offered further corroboration of the efforts to smear Marie L. Yovanovitch, the former ambassador to Ukraine, with what he described as “innuendo and threats coming from the highest levels,” before she was ousted from her post. He told lawmakers that Rudolph W. Giuliani, the president’s personal lawyer, had not only attacked Ms. Yovanovitch but “denigrated the whole embassy.”
The Judiciary Committee is expected to use the Intelligence Committee’s report and possibly other, earlier evidence of possible misconduct by the president detailed in the report by Robert S. Mueller III, the special counsel who investigated Russia’s election interference and the Trump campaign, to draft articles of impeachment in the coming weeks.
That schedule would put the House on track to potentially vote on articles of impeachment before lawmakers leave Washington for Christmas, setting up a trial in the Senate early next year.
“I think you want to know: What are you doing here? What are the standards? What are the rules?” Representative Zoe Lofgren of California, a senior Democrat on the panel, said, describing the purpose of next week’s first hearing.
The letter from Mr. Nadler initiated what is likely to be a high-stakes legal and political dispute between the two sides over what rights the president and his legal team should be afforded.
In modern times, the Judiciary Committee has allowed presidents facing similar proceedings an active role, inviting them to recommend witnesses for testimony, conduct cross-examinations and present a defense through their lawyers.
But whereas Mr. Clinton and former President Richard M. Nixon grudgingly engaged with Congress — at least to some extent — as it built impeachment cases against them, Mr. Trump’s White House has thus far responded only by declaring the House’s inquiry illegitimate and refusing to cooperate.
That has left Democrats uncertain about how to approach Mr. Trump’s role in the process. If the president is unwilling to engage with the allegations under debate or recommends that the committee call witnesses related to two unproven theories about Democrats that he pressed Ukraine to investigate, they are wary of offering him a prominent platform to broadcast what they believe amounts to counterprogramming, according to officials working on the matter, who spoke on condition of anonymity to describe their strategy.
But if they deny Mr. Trump his say, they fear, the process could lose legitimacy in the eyes of voters and Republicans in the Senate who would ultimately decide whether to convict Mr. Trump if the House impeaches him.
A key question will be whether Mr. Nadler, in consultation with Speaker Nancy Pelosi, chooses to exercise a provision Democrats included in the House rules governing the inquiry that allows him to deny the White House a role if he determines the president is unlawfully defying requests from Congress.
Earlier on Tuesday, Mr. Trump framed his decision to block key aides from testifying before Congress as a matter of preserving the powers of his office. He said he would otherwise be happy to let figures like Mr. Mulvaney; John R. Bolton, his former national security adviser; and Donald F. McGahn II, the former White House counsel, testify before the impeachment inquiry, implying without explanation that they could help his case.
“I am fighting for future Presidents and the Office of the President,” Mr. Trump wrote on Twitter. “Other than that, I would actually like people to testify.”
Mr. Trump was reacting to a federal court ruling on Monday holding that Mr. McGahn and other top presidential aides were not absolutely immune from congressional testimony as the White House has asserted. The Justice Department appealed that ruling on Tuesday, meaning that neither Mr. McGahn nor others named by Mr. Trump are likely to appear on Capitol Hill any time soon.
Emily Cochrane contributed reporting from West Palm Beach, Fla.