(CNN) A former top White House official on Thursday said that the effort to push Ukraine to open investigations into President Donald Trump's political rivals was a "domestic political errand" that came at the expense of US foreign policy.

"It struck me when (Wednesday), when you put up on the screen Ambassador Sondland's emails, and who was on these emails, and he said these are the people who need to know, that he was absolutely right," Hill said, referencing emails Sondland had sent to officials that included acting chief of staff Mick Mulvaney. "Because he was being involved in a domestic political errand. And we were being involved in national security foreign policy. And those two things had just diverged."

Hill added: "I had not put my finger on that at the moment, but I was irritated with him and angry with him that he wasn't fully coordinating. And I did say to him, 'Ambassador Sondland, Gordon, I think this is all going to blow up.' And here we are."

Hill testified on Capitol Hill on Thursday alongside David Holmes , the counselor for political affairs at the US Embassy in Ukraine, who was thrown into the middle of the impeachment inquiry after he told his boss, US diplomat Bill Taylor , that he overheard a call between Trump and US Ambassador to the European Union Gordon Sondland

The testimony from Hill and Holmes added to the roster of career government officials who have come forward in the impeachment inquiry to explain how the push for investigations from Trump's personal lawyer Rudy Giuliani moved forward outside normal government channels. Over five days of public testimony, multiple witnesses testified that the investigations into Trump's political opponents were conditioned on a White House meeting the Ukrainians wanted, as well as the releasing of $400 million in security aid that had been frozen.

"From May onwards, it became very clear that the White House meeting itself was being predicated on other issues, namely investigations and the questions about the election interference in 2016," Hill said.

'I could resist no more'

Hill and Holmes could be the final witnesses who testify before the House Intelligence Committee in the impeachment inquiry in which 17 witnesses appeared before impeachment investigators, with 12 officials testifying publicly at seven hearings over five separate days.

As Thursday's hearing moved into lawmaker questions, the questions to the witnesses slowed and lawmakers used their time to make their cases, passionate on both sides, for and against impeachment.

"The President did it. And the only question that remains is, what will we do?" said Rep. Denny Heck, a Washington Democrat.

"You guys want to be the laughingstock of history to impeach a President of the United States because he didn't take a meeting? Oh please, dear God, please undertake that," said Rep. Mike Turner, an Ohio Republican.

Fiona Hill, the National Security Council's former senior director for Europe and Russia, is sworn in to testify before the House Intelligence Committee in the Longworth House Office Building on Thursday in Washington.

Not all Republicans excused Trump's conduct, but none wavered when it came to impeachment. Rep. Will Hurd, a Texas Republican on the Intelligence panel who retiring, said Thursday that the July call was "inappropriate, misguided foreign policy," but he was opposed to impeachment.

"I have not heard evidence proving the President committed bribery or extortion," Hurd said.

House Democrats have not yet said that they are done with public hearings or depositions in the investigative phase of the impeachment inquiry. But House Intelligence Chairman Adam Schiff, a Democrat from California, delivered a closing argument on Thursday.

"I resisted going down this path for a long time. But I will tell you, why I could resist no more -- and it came down to this. It came down to, actually, came down to timing," Schiff said. "It came down to the fact that the day after (former special counsel) Bob Mueller testified ... Donald Trump is back on the phone asking another nation to involve itself in another US election. That says to me this President believes he is above the law, beyond accountability. And in my view there is nothing more dangerous than an unethical president who believes they are above the law."

Rebutting the 'fictional narrative' of Ukraine meddling

Hill's testimony corroborated several accounts offered by others about the events surrounding the July 25 call, which occurred after she left her role at the NSC. Hill mounted a forceful defense of another key impeachment inquiry witness, Lt. Col. Alexander Vindman , saying she grew concerned about his role on Ukraine only because things were shifting into a political realm.

"I did not feel he had the political antenna to deal with something that is straying into domestic politics. Not everyone is suited for that," Hill said. "That does not mean in any way that I was questioning his overall judgment, nor I was questioning in any way his substantive expertise. He is excellent on issues related to Ukraine, Belarus, and Moldova, on Russian defense issues."

As one of the final witnesses, Hill delivered a full-throated rebuttal to the "fictional narrative" pushed by Trump and his GOP allies, including during the impeachment inquiry hearings, that Ukraine interfered in the 2016 election. And she warned the House Intelligence Committee the Kremlin is prepared to strike again in 2020 and remains a serious threat to American democracy that the United States must seek to combat.

"Based on questions and statements I have heard, some of you on this committee appear to believe that Russia and its security services did not conduct a campaign against our country — and that perhaps, somehow, for some reason, Ukraine did," Hill said. "This is a fictional narrative that has been perpetrated and propagated by the Russian security services themselves."

Holmes' testimony also pushed back on several of the defenses offered by Trump and Republicans — that the evidence being offered is second-hand and hearsay, and that Ukrainian President Volodymyr Zelensky didn't feel pressure from Trump.

The Ukrainians still feel pressure to this day, Holmes testified, as they need US support while Zelensky tries to arrange a summit with Russian President Vladimir Putin.

"Although the hold on the security assistance may have been lifted, there were still things they wanted that they weren't getting, including a meeting with the President in the Oval Office," Holmes said. "Whether the security assistance hold continued or not, the Ukrainians understood that that's something the President wanted, and they still wanted important things from the President."

Holmes told lawmakers that he came forward with his account after reading reports on the impeachment inquiry noting "the lack of 'first-hand' evidence" and suggestions that the evidence being offered was "hearsay."

"I came to realize I had first-hand knowledge regarding certain events on July 26 that had not otherwise been reported, and that those events potentially bore on the question of whether the President did, in fact, have knowledge that those senior officials were using the levers of our diplomatic power to induce the new Ukrainian President to announce the opening of a criminal investigation against President Trump's political opponent," Holmes said.

'More than worthy of your attention'

Multiple witnesses have said that the moving forward on the 2016 election interference investigation -- along with a probe into former Vice President Joe Biden and his son, Hunter -- amounted to conditions placed on the country before roughly $400 million in military aid for the country was released and a key meeting in Washington between Trump and Zelensky could take place.

Both Giuliani and Trump have urged the Ukrainian government to announce probes into any role the country may have had in the 2016 elections, something Trump brought up himself in his now-infamous July phone call with Zelensky.

Hill disputes that argument -- with a warning for the future.

"We should all be greatly concerned about what the Russians intend to do in 2020," she said.

Rep. Devin Nunes, the ranking Republican on the House Intelligence Committee, pushed back on Hill's testimony. He suggested that Ukraine did in fact interfere in the 2016 election, while also pointing to the House Republican report on Russia election interference that was released last year. Nunes held up a copy of the 240-page report and passed them out to the witnesses.

"It's entirely possible for two separate nations to engage in election meddling at the same time, and Republicans believe we should take meddling seriously by all foreign countries, regardless of which campaign is the target," the California Republican said.

Republicans pointed to several disparaging comments Ukrainians made about Trump in the 2016 election. But Hill argued that individuals from many countries have criticized Trump, but his response to that criticism was unique to Ukraine.

Hill's testimony also included a subtle jab at some of her former colleagues who have refused to do what she is doing: appearing before the impeachment committees and detailing her experience. Hill said Trump had a right to be "aggrieved" by some of the criticisms, but she drew a clear distinction between those efforts and the systemic interference campaign that was run by Russia.

"I believe that those who have information that the Congress deems relevant have a legal and moral obligation to provide it," she says in her opening statement. Former national security adviser John Bolton, Hill's former boss, is among those who've refused to cooperate with impeachment investigators' request to testify.

"If the President, or anyone else, impedes or subverts the national security of the United States in order to further domestic political or personal interests, that is more than worthy of your attention," Hill told lawmakers. "But we must not let domestic politics stop us from defending ourselves against the foreign powers who truly wish us harm."

This story has been updated with additional developments Thursday.