“It is improper for the president of the United States to demand a foreign government investigate a U.S. citizen and political opponent,” Vindman told members of the House Intelligence Committee, referring to Trump’s request that Ukraine investigate his political rival, Joe Biden, and Biden’s son Hunter. The demands “had nothing to do with national security policy,” Vindman added.

Williams described the phone call as “unusual,” and said it “involved discussion of what appeared to be a domestic political matter,” rather than U.S. foreign policy goals in the region. The references to Biden “struck me as political in nature given that the former vice president is a political opponent of the president,” Williams said, but she declined to speculate about Trump’s motives.

Vindman defended his decision to report Trump’s comments to a White House lawyer “without hesitation,” adding: “It was my duty to report my concerns to the proper people in the chain of command.”

“It was also clear that if Ukraine pursued an investigation into the 2016 election, the Bidens, and Burisma, it would be interpreted as a partisan play,” Vindman said, referring to the Ukrainian energy company whose board Hunter Biden sat on. “This would undoubtedly result in Ukraine losing bipartisan support, undermine U.S. national security, and advance Russia’s strategic objectives in the region.”

Vindman and Williams sat side by side as House Democrats kicked off the second week of public impeachment hearings with Trump’s own national security aides who were troubled by Trump’s posture toward Ukraine. Lawmakers pressed them about why they felt Trump’s efforts to push his Ukrainian counterpart to investigate his political foes were inappropriate, and how they believed the campaign jeopardized U.S. national security.

Their testimony brings the inquiry closer to Trump than ever before — arming Democrats with firsthand accounts of Trump’s conversation with Zelensky amid criticism from Republicans that last week’s witnesses offered only “hearsay.”

Vindman responded directly to critics of his closed-door testimony, including the president, who referred to him as a “Never Trumper.” Other Trump allies have suggested that Vindman, an Army officer whose family came to the U.S. from the Soviet Union almost 40 years ago, holds dual loyalty.

Lt. Col. Alexander Vindman. | Susan Walsh/AP Photo

“I want to state that the vile character attacks on these distinguished and honorable public servants is reprehensible,” he said, adding: “In Russia, my act of expressing my concerns to the chain of command in an official and private channel would have severe personal and professional repercussions and offering public testimony involving the president would surely cost me my life.”

Republican lawmakers sought to question Vindman’s judgment, including whether he was motivated to come forward by a bias against Trump. Vindman rejected those suggestions, as Democrats sought to buttress both witnesses’ credibility by highlighting Vindman’s military honors and Williams’ work for George W. Bush’s presidential campaign.

Republicans stressed that Vindman was simply giving his personal opinion about the phone call, which the president’s allies have defended as proper. Lt. Gen. Keith Kellogg, Pence’s national security adviser and Williams’ direct supervisor, also sought to push back against the witnesses’ characterizations of the Trump-Zelensky phone call, saying he “heard nothing wrong or improper.”

Vindman disclosed to lawmakers that he discussed his concerns about the July 25 phone call with an official from the intelligence community, prompting Rep. Devin Nunes, the top Republican on the Intelligence Committee, to ask Vindman to name that individual. Intelligence Committee Chairman Adam Schiff (D-Calif.) stepped in to prevent Vindman from answering the question, saying it could resulting in identifying the whistleblower whose complaint spurred the impeachment inquiry.

“If the witness has a good-faith belief that this may reveal the identity of the whistleblower, that is not the purpose we’re here for,” Schiff said, prompting objections from GOP lawmakers.

Both officials also offered high-level insight into the confusion and alarm within the U.S. national security apparatus that followed Trump’s abrupt decision to freeze U.S. military aid to Ukraine, a key U.S. ally fending off Russian aggression.

Democrats on the House Intelligence Committee pressed them on whether they believed Trump and his allies were using the military aid, as well as a repeatedly delayed White House meeting for Ukraine’s president, as leverage to push the country to investigate Trump’s political enemies — the central claim that could form the basis of impeachment articles against the president.

Later Tuesday, lawmakers heard from Timothy Morrison, another senior NSC official who listened in on the July 25 call, and Kurt Volker, a former U.S. envoy for Ukraine negotiations who abruptly resigned in late September. Both witnesses were requested by Republicans, who have argued that they undercut claims that Trump did anything improper.

But their public testimony — in addition to the transcripts of their closed-door testimony — complicated that argument.

Morrison told lawmakers he had hoped Trump would give a “more full-throated statement of support” for Zelensky’s anti-corruption efforts during the July 25 phone call, while Volker said the allegations against Biden and his son are “self-serving and not credible.”

During his deposition last month, Morrison backed up testimony indicating a growing belief that a hold on military aid to Ukraine might have been used as leverage to press Zelensky to launch Trump’s favored investigations. Though he said he did not view Trump’s July 25 phone call as problematic, he later grew concerned about a possible quid pro quo, which he said was injected into the discussion by Gordon Sondland, the U.S. ambassador to the European Union, during a Sept. 1 meeting with Ukrainians in Warsaw.

During the hearing, the White House tweeted an excerpt from Morrison, Vindman’s former supervisor, who said during his closed-door testimony that he questioned Vindman’s “judgment.”

But in his public testimony Tuesday, Morrison said he did not intend for his previous comments to be taken as an attack on the “character or integrity” of his colleagues on the NSC.

Volker, meanwhile, testified about his contacts with Trump’s personal lawyer Rudy Giuliani and how the pair worked together to persuade Ukrainians to announce investigations connected to the Bidens and the 2016 election. But Volker suggested he saw no evidence of a quid pro quo — though he also acknowledged he was not involved in several of the meetings and conversations that have since been revealed in subsequent testimony.

“Mr. Volker is the definitive sort of story and narrative on this whole thing, and he has been clear all along: There was never any linkage of anything,” said Rep. Jim Jordan (R-Ohio), a top Trump ally. “And he was convinced all along the aid was going to get there.”

Volker’s appearance before the Intelligence Committee represented a significant moment: He was the first witness to speak with impeachment investigators behind closed doors and did not have the benefit of learning what a slew of subsequent witnesses attested to after his appearance. Since then, he has been described by other witnesses as playing a central role in some of the discussions about orchestrating a public statement by Zelensky announcing Trump’s preferred investigations.

Volker maintained that he did not view the push to investigate Burisma as an effort to tar Biden. He told lawmakers that he “should have seen” the connection and, “had I done so, I would have raised my own objections.”