With the start of the second week of public impeachment hearings under way, the country has now heard from a decorated war veteran and an aide to vice president Mike Pence.

Lt Col Alexander Vindman and foreign service officer Jennifer Williams kicked off proceedings on Tuesday, with both describing the potential perilous situation that could have been caused if American military aid was withheld from Ukraine — something Donald Trump allegedly threatened to do to coerce the nation into investigating 2020 rival Joe Biden.

These are some the key quotes from the hearing:

“I was concerned by the call. What I heard was inappropriate, and I reported my concerns to [National Security Council legal advisor John] Eisenberg. It is improper for the president of the United States to demand a foregin government to investigate a US citizen and a political opponent,” Lt Col Vindman said.

“It was also clear that if Ukraine pursued an investigation into the 2016 elections, the Bidens, and Burisma it would be interpreted as a partisan play. This would undoubtedly result in Ukraine losing bipartisan support, undermining US national security, and advancing Russia’s strategic objectives in the region."

Mr Vindman arriving in the hearing room Tuesday morning (AP)

Trump impeachment: Who's who in the Ukraine scandal Show all 26 1 /26 Trump impeachment: Who's who in the Ukraine scandal Trump impeachment: Who's who in the Ukraine scandal Donald Trump Accused of abusing his office by pressing the Ukrainian president in a July phone call to help dig up dirt on Joe Biden, who may be his Democratic rival in the 2020 election. He also believes that Hillary Clinton’s deleted emails - a key factor in the 2016 election - may be in Ukraine, although it is not clear why. EPA Trump impeachment: Who's who in the Ukraine scandal The Whistleblower Believed to be a CIA agent who spent time at the White House, his complaint was largely based on second and third-hand accounts from worried White House staff. Although this is not unusual for such complaints, Trump and his supporters have seized on it to imply that his information is not reliable. Expected to give evidence to Congress voluntarily and in secret. Getty Trump impeachment: Who's who in the Ukraine scandal The Second Whistleblower The lawyer for the first intelligence whistleblower is also representing a second whistleblower regarding the President's actions. Attorney Mark Zaid said that he and other lawyers on his team are now representing the second person, who is said to work in the intelligence community and has first-hand knowledge that supports claims made by the first whistleblower and has spoken to the intelligence community's inspector general. The second whistleblower has not yet filed their own complaint, but does not need to to be considered an official whistleblower. Getty Trump impeachment: Who's who in the Ukraine scandal Rudy Giuliani Former mayor of New York, whose management of the aftermath of the September 11 attacks in 2001 won him worldwide praise. As Trump’s personal attorney he has been trying to find compromising material about the president’s enemies in Ukraine in what some have termed a “shadow” foreign policy. In a series of eccentric TV appearances he has claimed that the US state department asked him to get involved. Giuliani insists that he is fighting corruption on Trump’s behalf and has called himself a “hero”. AP Trump impeachment: Who's who in the Ukraine scandal Volodymyr Zelensky The newly elected Ukrainian president - a former comic actor best known for playing a man who becomes president by accident - is seen frantically agreeing with Trump in the partial transcript of their July phone call released by the White House. With a Russian-backed insurgency in the east of his country, and the Crimea region seized by Vladimir Putin in 2014, Zelensky will have been eager to please his American counterpart, who had suspended vital military aid before their phone conversation. He says there was no pressure on him from Trump to do him the “favour” he was asked for. Zelensky appeared at an awkward press conference with Trump in New York during the United Nations general assembly, looking particularly uncomfortable when the American suggested he take part in talks with Putin. AFP/Getty Trump impeachment: Who's who in the Ukraine scandal Mike Pence The vice-president was not on the controversial July call to the Ukrainian president but did get a read-out later. However, Trump announced that Pence had had “one or two” phone conversations of a similar nature, dragging him into the crisis. Pence himself denies any knowledge of any wrongdoing and has insisted that there is no issue with Trump’s actions. It has been speculated that Trump involved Pence as an insurance policy - if both are removed from power the presidency would go to Democratic House Speaker Nancy Pelosi, something no Republican would allow. AP Trump impeachment: Who's who in the Ukraine scandal Rick Perry Trump reportedly told a meeting of Republicans that he made the controversial call to the Ukrainian president at the urging of his own energy secretary, Rick Perry, and that he didn’t even want to. The president apparently said that Perry wanted him to talk about liquefied natural gas - although there is no mention of it in the partial transcript of the phone call released by the White House. It is thought that Perry will step down from his role at the end of the year. Getty Trump impeachment: Who's who in the Ukraine scandal Joe Biden The former vice-president is one of the frontrunners to win the Democratic nomination, which would make him Trump’s opponent in the 2020 election. Trump says that Biden pressured Ukraine to sack a prosecutor who was investigating an energy company that Biden’s son Hunter was on the board of, refusing to release US aid until this was done. However, pressure to fire the prosecutor came on a wide front from western countries. It is also believed that the investigation into the company, Burisma, had long been dormant. Reuters Trump impeachment: Who's who in the Ukraine scandal Hunter Biden Joe Biden’s son has been accused of corruption by the president because of his business dealings in Ukraine and China. However, Trump has yet to produce any evidence of corruption and Biden’s lawyer insists he has done nothing wrong. AP Trump impeachment: Who's who in the Ukraine scandal William Barr The attorney-general, who proved his loyalty to Trump with his handling of the Mueller report, was mentioned in the Ukraine call as someone president Volodymyr Zelensky should talk to about following up Trump’s preoccupations with the Biden’s and the Clinton emails. Nancy Pelosi has accused Barr of being part of a “cover-up of a cover-up”. AP Trump impeachment: Who's who in the Ukraine scandal Mike Pompeo The secretary of state initially implied he knew little about the Ukraine phone call - but it later emerged that he was listening in at the time. He has since suggested that asking foreign leaders for favours is simply how international politics works. Gordon Sondland testified that Pompeo was "in the loop" and knew what was happening in Ukraine. Pompeo has been criticised for not standing up for diplomats under his command when they were publicly criticised by the president. AFP via Getty Trump impeachment: Who's who in the Ukraine scandal Nancy Pelosi The Democratic Speaker of the House had long resisted calls from within her own party to back a formal impeachment process against the president, apparently fearing a backlash from voters. On September 24, amid reports of the Ukraine call and the day before the White House released a partial transcript of it, she relented and announced an inquiry, saying: “The president must be held accountable. No one is above the law.” Getty Trump impeachment: Who's who in the Ukraine scandal Adam Schiff Democratic chairman of the House intelligence committee, one of the three committees leading the inquiry. He was criticized by Republicans for giving what he called a “parody” of the Ukraine phone call during a hearing, with Trump and others saying he had been pretending that his damning characterisation was a verbatim reading of the phone call. He has also been criticised for claiming that his committee had had no contact with the whistleblower, only for it to emerge that the intelligence agent had contacted a staff member on the committee for guidance before filing the complaint. The Washington Post awarded Schiff a “four Pinocchios” rating, its worst rating for a dishonest statement. Reuters Trump impeachment: Who's who in the Ukraine scandal Lev Parnas and Igor Fruman Florida-based businessmen and Republican donors Lev Parnas (pictured with Rudy Giuliani) and Igor Fruman were arrested on suspicion of campaign finance violations at Dulles International Airport near Washington DC on 9 October. Separately the Associated Press has reported that they were both involved in efforts to replace the management of Ukraine's gas company, Naftogaz, with new bosses who would steer lucrative contracts towards companies controlled by Trump allies. There is no suggestion of any criminal activity in these efforts. Reuters Trump impeachment: Who's who in the Ukraine scandal William Taylor The most senior US diplomat in Ukraine and the former ambassador there. As one of the first two witnesses in the public impeachment hearings, Taylor dropped an early bombshell by revealing that one of his staff – later identified as diplomat David Holmes – overheard a phone conversation in which Donald Trump could be heard asking about “investigations” the very day after asking the Ukrainian president to investigate his political enemies. Taylor expressed his concern at reported plans to withhold US aid in return for political smears against Trump’s opponents, saying: “It's one thing to try to leverage a meeting in the White House. It's another thing, I thought, to leverage security assistance -- security assistance to a country at war, dependent on both the security assistance and the demonstration of support." Getty Images Trump impeachment: Who's who in the Ukraine scandal George Kent A state department official who appeared alongside William Taylor wearing a bow tie that was later mocked by the president. He accused Rudy Giuliani, Mr Trump’s personal lawyer, of leading a “campaign of lies” against Marie Yovanovitch, who was forced out of her job as US ambassador to Ukraine for apparently standing in the way of efforts to smear Democrats. Getty Images Trump impeachment: Who's who in the Ukraine scandal Marie Yovanovitch One of the most striking witnesses to give evidence at the public hearings, the former US ambassador to Ukraine received a rare round of applause as she left the committee room after testifying. Canadian-born Yovanovitch was attacked on Twitter by Donald Trump while she was actually testifying, giving Democrats the chance to ask her to respond. She said she found the attack “very intimidating”. Trump had already threatened her in his 25 July phone call to the Ukrainian president saying: “She’s going to go through some things.” Yovanovitch said she was “shocked, appalled and devastated” by the threat and by the way she was forced out of her job without explanation. REUTERS Trump impeachment: Who's who in the Ukraine scandal Alexander Vindman A decorated Iraq War veteran and an immigrant from the former Soviet Union, Lt Col Vindman began his evidence with an eye-catching statement about the freedoms America afforded him and his family to speak truth to power without fear of punishment. One of the few witnesses to have actually listened to Trump’s 25 July call with the Ukrainian president, he said he found the conversation so inappropriate that he was compelled to report it to the White House counsel. Trump later mocked him for wearing his military uniform and insisting on being addressed by his rank. Getty Images Trump impeachment: Who's who in the Ukraine scandal Jennifer Williams A state department official acting as a Russia expert for vice-president Mike Pence, Ms Williams also listened in on the 25 July phone call. She testified that she found it “unusual” because it focused on domestic politics in terms of Trump asking a foreign leader to investigate his political opponents. Getty Images Trump impeachment: Who's who in the Ukraine scandal Kurt Volker The former special envoy to Ukraine was one of the few people giving evidence who was on the Republican witness list although what he had to say may not have been too helpful to their cause. He dismissed the idea that Joe Biden had done anything corrupt, a theory spun without evidence by the president and his allies. He said that he thought the US should be supporting Ukraine’s reforms and that the scheme to find dirt on Democrats did not serve the national interest. Getty Images Trump impeachment: Who's who in the Ukraine scandal Tim Morrison An expert on the National Security Council and another witness on the Republican list. He testified that he did not think the president had done anything illegal but admitted that he feared it would create a political storm if it became public. He said he believed the moving the record of the controversial 25 July phone call to a top security server had been an innocent mistake. Getty Images Trump impeachment: Who's who in the Ukraine scandal Gordon Sondland In explosive testimony, one of the men at the centre of the scandal got right to the point in his opening testimony: “Was there a quid pro quo? Yes,” said the US ambassador to the EU who was a prime mover in efforts in Ukraine to link the release of military aid with investigations into the president’s political opponents. He said that everyone knew what was going on, implicating vice-president Mike Pence and secretary of state Mike Pompeo. The effect of his evidence is perhaps best illustrated by the reaction of Mr Trump who went from calling Sondland a “great American” a few weeks earlier to claiming that he barely knew him. AP Trump impeachment: Who's who in the Ukraine scandal Laura Cooper A Pentagon official, Cooper said Ukrainian officials knew that US aid was being withheld before it became public knowledge in August – undermining a Republican argument that there can’t have been a quid pro quo between aid and investigations if the Ukrainians didn’t know that aid was being withheld. Getty Images Trump impeachment: Who's who in the Ukraine scandal David Hale The third most senior official at the state department. Hale testified about the treatment of Marie Yovanovitch and the smear campaign that culminated in her being recalled from her posting as US ambassador to Ukraine. He said: “I believe that she should have been able to stay at post and continue to do the outstanding work.” EPA Trump impeachment: Who's who in the Ukraine scandal Fiona Hill Arguably the most confident and self-possessed of the witnesses in the public hearings phase, the Durham-born former NSC Russia expert began by warning Republicans not to keep repeating Kremlin-backed conspiracy theories. In a distinctive northeastern English accent, Dr Hill went on to describe how she had argued with Gordon Sondland about his interference in Ukraine matters until she realised that while she and her colleagues were focused on national security, Sondland was “being involved in a domestic political errand”. She said: “I did say to him, ‘Ambassador Sondland, Gordon, this is going to blow up’. And here we are.” AP Trump impeachment: Who's who in the Ukraine scandal David Holmes The Ukraine-based diplomat described being in a restaurant in Kiev with Gordon Sondland while the latter phoned Donald Trump. Holmes said he could hear the president on the other end of the line – because his voice was so “loud and distinctive” and because Sondland had to hold the phone away from his ear – asking about the “investigations” and whether the Ukrainian president would cooperate. REUTERS

Lt Col Vindman said that he reported the 25 July phone call out of a “sense of duty”, and noted that he did so “privately” within the White House — he did not seek a national spotlight. Then, he returned to work.

This testimony is important on several fronts. It is a decorated war veteran with a long history serving the United States saying that Mr Trump’s efforts to pressure the Ukrainian government broke with normal US approach to international relations. But, it also illustrates that the pressure to investigate Joe Biden could have wide-ranging impacts including on US national security. In undermining the US position in Ukraine, that could also help Russia.

“I also recognise that my simple act of appearing here today, just like the courage of my colleagues who have also truthfully testified before this committee, would not be tolerated in many places around the world. In Russia, my act of expressing concern to the chain of command in an official and private channel would have severe personal, professional repercussions and offering public testimony involving the president would surely cost me my life,” Mr Vindman said.

This line came as Mr Vindman was describing to the committee his family’s history. Mr Vindman is an emigrant from the Soviet Union, whose family embraced military service after moving to the United States.

In this quote, Mr Vindman is drawing attention to his and his family’s dedication to service in the United States — it’s harder to attack a decorated war veteran with a Purple Heart on his chest — but also sticking up for the other individuals who have testified to the committee so far.

He is also drawing attention to the danger of Mr Trump’s attacks on witnesses, even if they don’t amount to the assassination he described would be the norm in Russia. Attacking dissidents is a major first step towards authoritarianism.

Ms Williams arrives before her testimony on Tuesday morning (Reuters)

“Chairman, without hesitation I knew that I had to report this to the White House counsel. I had concerns, and it was my duty to report my concerns to the proper people in the chain of command,” Mr Vindman said.

“As I said in my statement, it was inappropriate, it was improper for the president… to demand an investigation into a political opponent, especially a foreign power where there is, at best, dubious belief that this would be a completely impartial investigation. And that this would have significant implications if it became public knowledge, and it would be perceived as a partisan play, it would undermine our Ukraine policy, and it would undermine our national security.”

Mr Vindman is here laying out a powerful argument that contradicts a key Republican talking point, which is, why wouldn’t Mr Trump ask Ukraine for help with an investigation into the Bidens?

The answer, according to Vindman here, is that there is no reason to believe that any such Ukrainian investigation would be trustworthy, and would instead be “dubious” that the investigation would be impartial.

“Both of you recall president Zelensky in that conversation raising the issue, or mentioning Burisma, do you not?” asked Mr Schiff

“That’s correct,” said Ms Williams.

“Correct,” Mr Vindman said.

“And yet, the word Burisma appears nowhere in the call record that has been released to the public, is that correct? …. Do you know why that’s the case?” Mr Schiff asked.

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Mr Schiff is pointing out here that, in spite of Mr Trump’s frequent use of the call memo as absolute proof about what was said during the call, there are some omissions.

While Mr Vindman said it was not a significant omission, Mr Schiff pressed him further, and asked if Mr Zelensky bringing up the company was a signal that the Ukrainian had been prepped for the call, and to expect the issue to come up. He noted that it appears as though Mr Zelensky was therefore prepared to talk about the issue.

This would reinforce reporting and testimony that the issue was not brought up as a second thought during the 25 July phone call, and back up the idea that the phone call followed a months-long campaign to push for the investigation.

“No,” Mr Vindman said when asked if Mr Trump’s statements about conspiracy theories were included in prepared talking points for the president.

Mr Vindman testified that members of the National Security Council prepare talking points for the president and other officials on these calls, so that they can be prepared, and to ensure that they stick to US policy.

Trump impeachment: President mocks witnesses for wearing military uniform and bow tie

The witness said that that Mr Trump had the ability to choose to use the talking points or not, but that they were not consistent with what he had provided Democratic counsel Daniel Goldman that apparent conspiracy theories — including that Ukraine interfered in the 2016 election, and that “the server” was in Ukraine hands — mentioned were not based on talking points.

“So it is a part of US official policy that Ukraine should root out corruption even if president did not mention it… in that phone call?” Mr Goldman asked.

“Correct,” Mr Vindman said when asked if Mr Trump mentioned rooting out corruption in an April or July phone call between the US president and Mr Zelensky.

Mr Goldman was here walking Mr Vindman through another discrepancy between the call log provided by the White House, and the apparent actual substance of the conversation.

Mr Vindman noted that including that information on the log would be consistent with US policy, but that the issue was not brought up specifically by the president. This is interesting at least in part because Mr Trump did push specifically for other concerns that are not consistent with US policy — an investigation into a domestic political rival — but did not mention corruption itself.

“Dad, my sitting here today, in the US Capitol talking to our elected officials is proof that you made the right decision forty years ago to leave the Soviet UNion and come here to the United States of America in search of a better life for our family. Do not worry, I will be fine for telling the truth,” Mr Vindman said in his opening remarks.

Lt Col Vindman described in his opening remarks his family’s emigration to the United States from the former Soviet Union, and it is hard not to see the weight of the ending to this comment. In an impeachment effort that has not been light on accusations of intimidation, Lt Col Vindment is confident that he is safe describing his experience.

“It is natural to disagree and engage in spirited debate, this has been our custom since the time of our Founding Fathers, but we are better than callow and cowardly attacks,” Lt Col Vindman said.

Lt Col Vindman here appears to be referencing attempts to intimidate him and others in the impeachment inquiry, and casts the effort as dishonorable.

The Trump-Zelensy call was “unusual” because “it involved discussion of what appeared to be a domestic political matter,” said Ms Williams.

Ms Williams, like Lt Col Vindman, had served American interests abroad longer than during just this presidency. And, she said that she had sat in on many presidential calls, but had not encountered anything close to Mr Trump’s effort to push for an investigation into Mr Biden.

“Representative Jordan, I did my job,” Lt Col Vindman said.

Congressman Jim Jordan and Lt Col Vindman clashed over his job performance, with the Republican claiming that his former boss — Dr Fiona Hill — had expressed concern with his job performance.

Lt Col Vindman responded to the accusations about his former boss by pulling out his last performance review from her, which he read: “Alex is top 1 per cent military officer and the best Army officer I have worked with in my 15 years of government service. He is brilliant, unflappable, and exercises excellent judgement’ — I’m sorry — ‘Was expemplary during numerous visits,’ so forth and so on. I think you get the idea.”

When attacked for consulting a lawyer with his concerns about Mr Trump’s call, Mr Vindman explained that he “did my core function, which is coordination”, and that his lawyer ultimately told him not to speak to anybody.

When attacked further by Mr Jordan, who complained that he would not tell him who the whistleblower is, Lt Col Vindman told him he simply did his job.

“I call myself never partisan,” Lt Col Vindman said.

Lt Col Vindman and Ms Williams were both asked if they consider themselves “never Trumpers” — meaning, people who would never support Mr Trump no matter the circumstances.