WASHINGTON — President Donald Trump presented little in the way of defense in the opening phase of his impeachment proceedings.

He refused to give Congress documents. He ordered subordinates to defy subpoenas. And he issued blanket proclamations of his innocence, over Twitter and in exchanges with reporters, without testifying under oath on Capitol Hill.

Meanwhile, as Democrats moved one step closer to a House floor vote on impeachment that they expect to hold before Christmas, a string of current and former administration officials collectively described for the House Intelligence Committee over the last two weeks how the president directed a concerted effort to aid his own re-election efforts at the expense of U.S. national security interests.

Specifically, they said he deployed several Cabinet officials, White House chief of staff Mick Mulvaney and his personal lawyer Rudy Giuliani on a mission to force Ukrainian President Volodymyr Zelenskiy to announce probes of former Vice President Joe Biden and a discredited theory that his own country framed Russia for interfering in the 2016 election, withholding $391 million in taxpayer dollars and a White House meeting to aid that effort.

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"The question for impeachment is abuse of power," said Kim Wehle, a professor at the University of Baltimore School of Law who worked on independent counsel Kenneth Starr's investigation of President Bill Clinton.

"There is no Trump narrative laying out a legitimate public policy rationale for how the president, through Giuliani, treated Ukraine — by refusing a meeting and withholding aid needed to fight Russia — other than entrenching his own power."

Trump's counteroffensive was left to Republican allies, who spent most of their time during the hearings suggesting that the president was justifiably concerned that Ukraine had framed Russia for interfering in the 2016 election to harm him, and that matters involving Biden merited an investigation announcement ordered up by the president and pursued by senior executive branch officials.

Fiona Hill, the former deputy national security adviser under Trump, testified Thursday that the idea that Ukraine interfered in the 2016 campaign is a "fictional narrative" that was "perpetrated and propagated" by Russia.

Republicans on the committee repeatedly noted that none of the witnesses were able to cite Trump directly conditioning aid on Ukraine opening political investigations, and the ambassador to the European Union, Gordon Sondland, testified that the president told him "no quid pro quo" when Sondland asked what the president wanted from Ukraine in order to free up the money in early September.

However, the White House was already aware at that point of a whistleblower complaint making its way through the intelligence community's inspector general's office and the Justice Department that alleged the president had improperly conditioned the money on the announcement of the probes.

David Holmes, a U.S. diplomat posted in Kyiv who also testified Thursday, said that former national security adviser John Bolton told an aide to Zelenskiy on Aug. 27 that the unfreezing of military aid was conditioned on the Ukrainian president making a favorable impression on Trump at a planned meeting in Warsaw.

"By this point, however, my clear impression was that the security assistance hold was likely intended by the president either as an expression of dissatisfaction that the Ukrainians had not yet agreed to the Burisma/Biden investigation or as an effort to increase the pressure on them to do so," Holmes testified.

Ultimately, though, several of the witnesses who listened to a July 25 phone call between Trump and Zelenskiy — or later read a reconstructed White House transcript of it — concluded that the president, who already had put a stop on the money, was connecting the assistance to the "favor" he asked Zelinskiy to do in looking into Biden and the election interference issue.

"We heard Democrats lay out the elements of bribery through witnesses," Wehle said of the possibility of impeachment articles that go beyond "high crimes and misdemeanors" based on abuse of power. "And we know they are concerned about witness intimidation and obstruction of subpoenas."

Much of that remains to be determined, though.

House officials tell NBC News that the Judiciary Committee, which is responsible for drafting articles of impeachment, is likely to take up the next stage of the process after Thanksgiving, which may include hearings of its own.

"We could have a Judiciary hearing as early as that first week after Thanksgiving," a senior Democratic aide familiar with internal party discussions said.

The process there would be relatively quick, according to a House Democratic leadership aide.

"I think they're very happy," the aide said of party leaders. "We probably would vote on it on the floor the third week of December."

They say they are satisfied that they have built the case that the president's actions merit impeachment — but have their work cut out for them in swaying 20 or more Republicans to vote to oust him.

So far, no Senate Republican has said Trump's conduct justifies removal from office.