House investigators staged another marathon day of public impeachment hearings on Tuesday, featuring a career military official defending his years of service from GOP questions of loyalty as well as a top diplomat, hand-picked by Republicans, who shifted his testimony to offer a more critical view of 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’s contacts with Ukraine.

Lt. Col. Alexander Vindman Alexander VindmanImpeachment witness Alexander Vindman calls Trump Putin's 'useful idiot' The Hill's Morning Report - Sponsored by The Air Line Pilots Association - Trump, Biden renew push for Latino support Strzok: Trump behaving like an authoritarian MORE, a Ukraine specialist on the National Security Council (NSC), clashed with Republicans during the hearing of the Intelligence Committee, where he provided a first-hand account of the July 25 call between Trump and Ukraine President Volodymyr Zelensky.

Trump had pressed Zelensky to launch investigations that could have benefited Trump politically — the episode at the heart of the House impeachment inquiry — and Vindman characterized the pressure campaign as “improper.”

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“It is improper for the president of the United States to demand a foreign government investigate a U.S. citizen and political opponent,” he said.

Lawmakers also heard from Kurt Volker Kurt VolkerGOP senators request details on Hunter Biden's travel for probe Yovanovitch retires from State Department: reports Live coverage: Senators enter second day of questions in impeachment trial MORE, the former special envoy to Ukraine, who dismissed outright the GOP claims that 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 had called for a Ukraine prosecutor’s dismissal because of his son’s role in Burisma, a Ukrainian energy company. It is, Volker said, a “conspiracy theory.”

Volker’s testimony was notable because Republicans expected him to be a friendly witness for Trump. Indeed, House Republicans have said for weeks that Volker had “exonerated” Trump in his closed-door deposition last month, when he’d testified that the White House’s hold on U.S. military aid to Ukraine was “not significant.”

But his Tuesday testimony offered a snapshot of a diplomat who had “cringed” upon hearing how his role in Ukraine was perceived by other top diplomats, particularly his willingness to associate with 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, Trump’s personal lawyer, who was leading the charge to secure the investigations the president sought.

And Volker revised his previous testimony slightly to acknowledge that 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, U.S. ambassador to the European Union, had floated a reference to “investigations” in a July 10 meeting with top Ukrainian officials — a reference Volker had denied in his closed-door deposition on Oct. 3.

All in all, it added up to another long day for the White House, which fought back by questioning the credibility of certain witnesses and attacking the Democrats conducting the impeachment investigation.

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“Buried among the witnesses’ personal opinions and conjecture about a call the White House long ago released to the public, both witnesses testified the July 25 transcript was ‘accurate’ and nothing President Trump has done or said amounts to ‘bribery’ or any other crime,” press secretary Stephanie Grisham Stephanie GrishamIvana Trump on Melania as first lady: 'She's very quiet, and she really doesn't go to too many places' The Hill's 12:30 Report: Trump uses White House as campaign backdrop Coronavirus tests not required for all Melania Trump speech attendees: report MORE said in a statement.

There were no earth-shattering revelations in the roughly 11 hours of testimony, but lawmakers in both parties left claiming new ammunition in the battle over Trump’s future.

Vindman said Trump’s request for “a favor” from Zelensky — a reference to the politically tinged investigations — amounted to a “demand.” Those details support the allegations from Democrats that Trump had abused his office by enlisting a foreign power to boost his political prospects at home — the charge at the root of the impeachment investigation.

Republicans sought to challenge his interpretation, particularly after Vindman said he leaned on his understanding of “military culture” that when a higher-up makes an ask, however politely, it is not a mere suggestion.

“Representative, when a superior makes a request, that’s an order,” Vindman testified.

“I think it’s nonsense,” shot back GOP Rep. Chris Stewart Christopher (Chris) Douglas StewartAtlanta Wendy's 911 call the night of Rayshard Brooks's death released Tyler Perry offers to pay for funeral of Rayshard Brooks Current, former NHL players form diversity coalition to fight intolerance in hockey MORE (Utah), who served for more than a decade in the Air Force. “I was in the military. I could distinguish between a favor and an order and demand and so could my subordinates. And I think President Zelensky did as well.”

Vindman faced questions from Republicans about whether he may have had dual allegiances to other countries or if he was the source of leaks to outside press. In particular, GOP counsel Stephen Castor pressed about offers by Ukrainians to have Vindman serve as the country’s minister of defense.

Vindman, whose family fled the Soviet Union when he was a toddler, rejected the entreaties, saying that he was an American. He also notified his chain of command after they occurred. But when pressed further by Castor whether he “left the door open” to accepting these offers, Vindman shot down the idea as being “comical.”

“I did not leave the door open at all. It is pretty funny for a lieutenant colonel of the United States Army, which really isn’t that senior, to be offered that illustrious of a position,” Vindman replied.

Republicans leaned heavily on the testimony of Tim Morrison, a top aide at the NSC who was also on the July 25 phone call. Morrison had raised concerns about that call at the time, but not, he said, because he thought Trump had acted inappropriately.

“I feared at the time of the call on July 25 how its disclosure would play in Washington’s political climate,” he testified. “My fears have been realized.”

During his public testimony, Volker sought to distance himself from the controversy involving the Trump administration’s decision on Ukraine.

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Volker, who left his post shortly after the White House released a rough transcript of Trump’s July 25 phone call with Zelensky, testified that “at no time” was he aware of — nor did he knowingly take part in — an effort to investigate Biden. Rather, he said that he now can link the requests for corruption investigations to the efforts to dig up dirt on Biden, following the testimonies from other witnesses.

“In hindsight, I now understand that others saw the idea of investigating possible corruption involving the Ukrainian company, ‘Burisma,’ as equivalent to investigating former Vice President Biden,” Volker testified.

“I saw them as very different — the former being appropriate and unremarkable, the latter being unacceptable. In retrospect, I should have seen that connection differently, and had I done so, I would have raised my own objections,” Volker said.

The diplomat said he learned about the Biden component only after he saw the summary readout of the July 25 call, released by the White House in September.

And Volker also said he “rejected” the “conspiracy theories” raised by Giuliani during a one-on-one meeting July 19, all while insisting he had no knowledge of an effort to investigate Biden within the Trump administration.

“At the one in-person meeting I had with Mayor Giuliani on July 19, Mayor Giuliani raised, and I rejected, the conspiracy theory that Vice President Biden would have been influenced in his duties as vice president by money paid to his son,” Volker said in his opening remarks at a House impeachment hearing Tuesday.

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“As I testified previously, I have known Vice President Biden for 24 years. He is an honorable man and I hold him in the highest regard,” Volker said.

Jennifer Williams, a top national security aide to Vice President Pence, also testified Tuesday that she viewed Trump’s request to open an investigation as “unusual” because it “involved discussion of what appeared to be a domestic political matter,” which was the mention of Biden, a top 2020 political rival of Trump. Williams was labeled by Trump as a “never Trumper” after she offered her view to House investigators last month.

Trump has repeatedly defended the call as “perfect,” insisting that his mention of Biden was related to his effort to weed out “corruption” in Kyiv and maintaining that it had nothing to do with the 2020 presidential election.

The public testimony of these four witnesses comes before Sondland, who is slated to testify on Wednesday. The Trump-picked diplomat is viewed as a wild card, as both critics of Trump and defenders of the president are unsure whether he will help or protect the man occupying the Oval Office.