Updated at 8:40 p.m ET

Two witnesses called by Republicans in the House impeachment inquiry testified Tuesday, indicating they had reservations over the content of President Trump's July 25th phone call with the president of Ukraine, and his desire to investigate former Vice President Joe Biden.

Capping a long day of testimony, the House Intelligence committee heard from Kurt Volker, the former U.S. Special representative for Ukraine, and Tim Morrison, a former National Security Council aide in the afternoon session. Lawmakers earlier heard from two other witnesses who listened firsthand to the call with President Volodymyr Zelenskiy, a key moment in the Ukraine affair.

The phone call with Ukraine's president that President Trump has repeatedly characterized as "perfect" was called "improper" by a National Security Council staff member Lt. Col. Alexander Vindman, an Army foreign area officer who serves on the National Security Council. Jennifer Williams, a foreign service officer detailed to the staff of Vice President Pence also testified about the July call.

Volker was at the center of the alternate policy channel for Ukraine run by Trump's personal lawyer Rudy Giuliani, and Volker helped broker an important meeting between Giuliani and an aide to Zelenskiy this summer.

In his opening statement, Volker changed some key aspects of his testimony behind doors last month, saying "a great deal of additional information and perspectives have come to light" since then. He said he did not know of any linkage between the hold on U.S. military aid to Ukraine and the country's pursuing investigations, and he said he did not convey such a linkage to the Ukrainians.

Volker also initially said there was no discussion in a July 10 meeting between then-national security adviser John Bolton and Ukrainian official Alex Danylyuk of Trump's personal attorney Rudy Giuliani's investigation of the Bidens.

But in Tuesday's opening statement, Volker testified "As I remember, the meeting was essentially over when Ambassador Sondland made a generic comment about investigations." Volker continued "I think all of us thought it was inappropriate; the conversation did not continue and the meeting concluded."

Volker said he did not understand that others believed that any investigation of the Ukrainian energy company Burisma, "was tantamount to investigating Vice President Biden."

The former Ukraine envoy said he had known Biden for 24 years, calling him "an honorable man and I hold him in the highest regard."

Volker also said that he didn't think that "raising the 2016 elections or Vice President Biden or these things I consider to be conspiracy theories that have been circulated by the Ukrainians" should be pursued as part of the U.S. security strategy with Ukraine.

Morrison was also among those who heard the Trump-Zelenskiy call firsthand when it happened, and although he testified that he was concerned about what might have happened if it became public, he saw nothing illegal.

He testified Tuesday that he was disappointed in the call between the two presidents, explaining he was "hoping to hear a more full-throated" endorsement of Zelenskiy's reform agenda from Trump.

Asked by majority counsel Daniel Goldman if he agreed that asking a foreign government to investigate a domestic political rival is inappropriate, Morrison responded, "it's not what we recommended the president discuss."

After the first panel of the day wrapped up, White House press secretary Stephanie Grisham said Vindman and Williams' testimony provided nothing new, calling the proceedings "illegitimate."

"However, 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," her statement said. "Today's hearing only further exposes that Chairman Schiff and the Democrats are simply blinded by their hatred for Donald Trump and rabid desire to overturn the outcome of a free and fair election."

"Improper"

Vindman testified Tuesday that he was concerned by the call, because "what I heard was improper," and said that he reported his concerns to NSC lawyer John Eisenberg.

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

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Williams, for her part, has told House investigators she thought Trump's requests were "unusual and inappropriate," but did not relay her concerns to her supervisor, Lt. General Keith Kellogg, Pence's National Security Advisor.

Kellogg issued a statement that he "heard nothing wrong or improper on the call. I had and have no concerns."

Vindman also said in earlier closed-door testimony that Eisenberg moved the official record of the call onto a highly classified system that few could access — a decision that Vindman called a departure from protocol.

Vindman stated that it was his view that Trump demanded Zelenskiy conduct an investigation into the activities of former vice president and potential 2020 opponent Joe Biden and his son Hunter's involvement in Ukraine.

Vindman said there was a "power disparity" between the two presidents and that because of his military culture, "a request, no matter how politely expressed," is an order or demand.

Trump has argued that there was no pressure on the call.

"Do not worry"

Testifying in his military uniform, Vindman movingly referred to his father, who fled the Soviet Union with his family to the U.S.: "Dad, I'm sitting here today in the U.S. Capitol, talking to our elected officials is proof that you made the right decision 40 years ago to leave the Soviet Union." Vindman continued, "Do not worry, I will be fine for telling the truth."

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Asked later why he was confident that he could tell his father not to worry about challenging the president, Vindman responded, "Here, right matters."

It was followed by applause in the hearing room.

Vindman also lashed out at the attacks on the three witnesses who testified before the panel last week. "The vile character attacks on these distinguished and honorable public servants is reprehensible," Vindman said. He added, "We are better than personal attacks."

As Vindman testified, the official White House Twitter account tweeted criticism of Vindman from his former boss, Morrison, who is testifying later Tuesday. The tweet quoted Morrison as saying "I had concerns about Lieutenant Colonel Vindman's judgment."

Tussle over potential whistleblower identity

Intelligence Committee Chairman Adam Schiff, D-Calif., interrupted Republican ranking member Devin Nunes' questioning of Vindman when Nunes appeared to try to get Vindman to identify the whistleblower.

Vindman was testifying that he spoke to two people outside of the White House about providing a readout of the July 25 call. He said one was Deputy Assistant Secretary of State George Kent, and he identified the other as a member of the intelligence community.

When Nunes pressed Vindman for the name of the agency, Schiff interjected. "The whistleblower has the statutory right to anonymity," he said. "These proceedings will not be used to out the whistleblower."

Vindman said he did not know the whistleblower, whose official complaint sparked the impeachment inquiry, but said his counsel advised him not to answer specific questions about who he spoke with in the intelligence community.

During the exchange, Vindman also corrected Nunes when Nunes called him "Mr. Vindman."

"Ranking member, it's Lt. Col. Vindman, please."

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Attacks on "loyalties"

Under questioning from GOP counsel Steve Castor, Vindman acknowledged that he was asked three times by Ukrainian officials to be the country's defense minister. Vindman said he dismissed the offer each time and said he told his chain of command and the "appropriate counterintelligence folks about the offer."

Vindman testified that it would be "a great honor," but that "I'm an American, I came here when I was a toddler, and I immediately dismissed these offers, did not entertain them."

Rep. Jim Himes, D-Conn., told Vindman the questions about the Ukrainian offer "were designed exclusively to give the right-wing media the opening to attack your loyalties." He added, "It's the kind of thing you say when you're defending the indefensible."

Asked about a Trump tweet that labeled her a "never Trumper," Williams said "It certainly surprised me. I didn't expect to be called out by name."

Asked if he were a "never Trumper," Vindman replied, "I would call myself never partisan."

The president's response was the second time he has posted about a witness in the ongoing hearings, following a tweet last week about Ambassador Marie Yovanovitch.

Trump's ongoing responses to the impeachment inquiry have raised questions about whether they could become the subject of eventual articles of impeachment.

Democrats say the president is trying to dissuade people from talking publicly.

"I absolutely believe this is witness intimidation," Rep. Joaquin Castro, D-Texas, told CNN on Monday.

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