The third day of public impeachment inquiries yielded some key information related to Donald Trump’s efforts to coerce Ukraine into opening an investigation into a domestic political rival, this time from Lt Col Alexander Vindman and Jennifer Williams.

The two witnesses are the first who were on the infamous 25 July phone call between Mr Trump and Ukrainian president Volodymyr Zelensky, when the American asked for a favour from his Ukrainian counterpart. Later testimony involved Kurt Volker, a former US special representative for Ukraine negotiations, and Tim Morrison, a political advisor who was on the White House National Security Council for a time.

While perhaps light on fireworks, the hearings provided valuable insight into the Republican strategy when it comes to the impeachment investigation, while also reinforcing several key points we’ve already heard about.

Here’s what you need to know:

During the hearings, Lt Col Vindman’s integrity was frequently questioned – and affirmed. Lt Col Vindman is an Army war veteran who has devoted his life to serving the United States, and he made sure the hearing room knew it. He wore formal military attire for his testimony, and delivered a strong opening statement in which he told members of Congress that his family had moved to the United States from the former Soviet Union — and it was one of the best decisions they could have made.

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

During his testimony, the colonel even corrected ranking member Devin Nunes to refer to him by his title. “Ranking member, it’s Lt Col Vindman, please,” he said.

Lt Col Vindman also faced the insinuation from Republican counsel Steve Castor that he had duelling loyalties, in spite of his decorated military service. Mr Castor asked Mr Vindman if he had been offered positions with the Ukrainian government — he had, he said, but noted that he had turned them down and notified appropriate US officials about the offer.

“I’m an American, I came here when I was a toddler, and I immediately dismissed these offers. I did not entertain them,” he said. He later called the idea “funny” that he would take the position.

Lt Col Vindman confirmed key points in the impeachment investigation so far — and laid out their importance. The Army veteran’s testimony not only confirmed key aspects of the scandal plaguing the Trump administration, he also took things a step further and said he believed Mr Trump’s attempt to force a foreign leader to investigate a domestic political rival would have devastating consequences.

He said he believed any investigation would yield “dubious” results, and would also imperil US foreign interests and allies. He said during his testimony that keeping US military aide from Ukraine over an investigation into Joe Biden risked Ukrainian sovereignty, European Union security, and that it blatantly diverged from talking points prepared for the president by his national security staff.

Jennifer Williams and Alexander Vindman prepare to testify at the impeachment hearings into Donald Trump (AP)

Republicans once again attempted to unmask the whistleblower’s identity. House Intelligence chairman Adam Schiff and the committee’s Republicans once again sparred over the identity of the whistleblower. That identity is not public, and is protected under federal law.

Republicans have sought to unmask this individual in their attempt to smear the accusations. But, they have also noted that the whistleblower was not sitting in on the 25 July phone call — as opposed to Lt Col Vindman and Ms Williams, who did.

Witnesses once again addressed debunked conspiracy theories about the Bidens and 2016. Both Lt Col Vindman and Ms Williams testified that there is no evidence to suggest Joe Biden did anything wrong while dealing with Ukraine as vice president, in spite of any appearance of conflict of interest presented by his son, Hunter Biden, working for the energy company Burisma.

Lt Col Vindman was also asked to address the conspiracy theory surrounding CrowdStrike, which he said was completely false and contrary to unanimous findings by the US intelligence community that Russia was responsible for 2016 election interference.

Crowdstrike is a Silicon Valley-based cybersecurity firm that has conducted major cyber investigations, and has become a favourite boogeyman of the right wing conspiracy machine. Those right-wing accusations include assertions that the company helped Democrats cover up breaches.

Lt Col Vindman cast attacks on impeachment witnesses as ‘vile’ attempts against ‘honourable’ public servants. The comment came during Lt Col Vindman’s opening remarks, in which he took “a moment to recognise the courage of my colleagues who have appeared and are scheduled to appear before this committee.”

In an apparent reference to Mr Trump’s real-time attacks on former Ukraine ambassador Marie Yovanovitch last week, when he degraded her service in a tweet that was later read to her during her testimony and described as “intimidating”, he said: “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 told his dad not to worry about his safety, because they now live in America. One of the most striking moments of the testimony came during prepared opening remarks, in which Lt Col Vindman noted that his family had emigrated to the United States from the former Soviet Union over 40 years ago.

In that time since, they have established themselves in the United States — including, notably, Lt Col Vindman’s ascent to a position in the White House national security council.

“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 United States of American in search of a better life for our family. Do not worry, I will be fine for telling the truth.”

Ms Williams said the Trump-Zelensky call was ‘unusual’ because it included domestic politics. Ms Williams testified that she had served in both Democratic and Republican administrations, before being hired onto Mr Pence’s team.

She was among those on the infamous 25 July phone call, and said that she thought that the call was “unusual because, in contrast to other presidential calls I had observed, it involved discussion of what appeared to be a domestic political matter.”

Mr Volker — whom Republicans asked for specifically — did not turn out to be the witness the GOP had hoped for. Mr Volker, during the second round of testimony, said that he has known Mr Biden for "24 years", and that "the suggestion that he would be influenced in his duties as vice president by money for his son simply has no credibility to me. I know him as a man of integrity and dedication to our country." This undermines a key Republican talking point during this entire thing, which was that an investigation into Mr Biden was called for, and therefore OK for the president to push for from Ukraine.

Mr Volker essentially changed key portions of his testimony, compared to what we knew he said in private testimony. Another thing worth noting is that he now recognises that the "investigations" actually came up during a July 10 meeting he had with Gordon Sondland, the ambassador to the European Union who was brought in to push Ukraine policy (and who is set to testify on Wednesday).

He also testified that he did not view an investigation as "a condition" for released military aide, which contradicts previous testimony.