Days after a decorated Army lieutenant colonel offered damaging testimony about president Donald Trump’s conduct on a July phone call with Ukraine’s leader, Trump stood on the South Lawn and issued a vague but ominous warning.

“You’ll be seeing very soon what comes out,” Trump said, referring to the officer, lieutenant colonel Alexander Vindman.

The US president was not more specific. But an attack on Mr Vindman’s character and motives was already making its way from the dark corners of Mr Trump’s social media following to the front lines of the impeachment battle.

One day earlier, right-wing commentator Jack Posobiec had retweeted a lengthy thread by a Florida man — a fan of QAnon, a fringe conspiracy about the “deep state” — claiming to have witnessed Mr Vindman “bash America” in a conversation with Russian officers during a joint military exercise in Germany in 2013.

That accusation was unsubstantiated and has been rejected by some of the colonel’s colleagues. Even so, Mr Posobiec’s post was retweeted by Trump’s son and chief defender, Donald Trump Jr, driving it through conservative social media circles and onto pro-Trump websites, whose stories the younger Mr Trump promoted to his 4 million followers.

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

“Anyone who’s been watching for the past three years is not at all surprised that this would be their ‘star witness,’” the president's son posted about Mr Vindman, who had testified that he was concerned about the linking of US military aid to Ukraine with an investigation of Trump’s political rival.

While the White House has scrambled to mount an organised response to the House impeachment inquiry — there is no consistent message from Mr Trump’s team and little formal guidance to surrogates — Twitter has become the president’s war room. The president and his supporters, including his family, have used Twitter to frame his defence, torch his Democratic inquisitors and try to undermine public officials, like Mr Vindman, who have testified against him.

It is hard to discern how the 6-year-old comments attributed to the officer affect the veracity of his testimony on Capitol Hill, which aligns with that of numerous other witnesses.

But by questioning the colonel’s loyalties, partisans who are spreading the story uncritically to millions of Americans leave the impression he is somehow not to be believed.

The attack emerged late on Halloween night, when a retired Army officer, Jim Hickman, claimed he had overheard Vindman — a major at the time who was chatting with Russian soldiers during a military exercise — laugh “about Americans not being educated or worldly” and talking up “Obama and globalism to the point of uncomfortable”.

Mr Hickman said he took the major aside and reprimanded him.

Through his lawyer, Michael Volkov, Mr Vindman declined to comment.

Mr Hickman, a former lieutenant colonel whose service record indicates he served in Afghanistan and earned a Purple Heart, at some point took an interest in QAnon.

A review of his past tweets found more than 100 in which he recirculated or commented on QAnon-related theories, including hoaxes about Satanism and paedophilia, and until recently he had the hashtag #Q in his profile.

Reached for comment, Mr Hickman said he did not believe in QAnon but found it “interesting.”

“I do think it’s actually been pretty accurate on predicting a lot of things,” he said.

He has also tweeted strident pro-Trump, anti-Democratic themes, writing, “It’s incredible how evil the Democrat party is”.

Mr Vindman leaving a closed-door meeting after testifying for 10 hours as part of the impeachment inquiry (AP)

A week before going public with his story about Vindman, he retweeted a Trump supporter urging “STOP IMPEACHMENT! STOP THIS COUP!”

In a Twitter thread, Mr Hickman, who said he was disabled from combat injuries and living in Florida, said he had helped manage joint exercises in Germany involving US and Russian soldiers.

He met Mr Vindman there in 2013, he said.

Mr Vindman referred to himself as a patriot during closed-door testimony in the house last month and said he had reported concerns about the president and his inner circle’s conduct out of a “sense of duty”.

The colonel received a Purple Heart after being injured by an improvised explosive device in Iraq.

Several officials have publicly defended Mr Vindman since his testimony emerged. General Joseph Dunford, the former chairman of the Joint Chiefs of Staff, has called the colonel “a professional, competent, patriotic and loyal officer”.

Michael McFaul, the former ambassador to Russia, has said he had worked with the colonel “and interacted with him in front of Russian officers. He never once said anything near what this ‘retired Army officer’ claims”.

As the tale gained attention on Twitter and received pushback from some users who questioned it, a new Twitter account popped up with the name Thomas Lasch, tweeting that he had worked with Mr Hickman and remembered the 2013 episode.

Mark Hertling, a retired general who was suspicious of the pair and contacted them through direct messaging, later tweeted: “They are who they say they are.” But he added that “LTC Hickman and I agreed to disagree on LTC Vindman and many other things.”

In an interview, Mr Hertling, who commanded the US Army in Europe, said that a number of things about Mr Hickman’s recollections did not add up, including his claim of hearing what Mr Vindman, who was born in Ukraine, said to Russian soldiers.

“Vindman would’ve been speaking to Russian soldiers in Russian, not English,” he said. “Russians, when they come to these exercises, they don’t speak English — they take pride in it.”

Mr Hertling added: “I asked Hickman about that, and he said, ‘Well, they were going back and forth between Russian and English.’”

An effort to reach Mr Lasch was unsuccessful. At his home in Homosassa, Florida, Hickman said, “All I want is the truth to get out”.

Within a day of Mr Vindman’s testimony, conservative media figures on Fox News and elsewhere, as well as Republican surrogates like Rudy Giuliani, raised questions about whether the Ukrainian-born colonel had “dual loyalties”. Some even pushed innuendo that he could be some sort of spy for Ukraine.

But those who know and have worked with Mr Vindman have provided a different account.

They said that Mr Vindman, then a military attache, was assigned to meet with Russians and gather whatever intelligence he could. He spoke to the Russians in Russian, did not denigrate the US and reported back everything he heard, according to a person briefed on the episode, speaking on the condition of anonymity because the colonel had not publicly testified.

Mr Vindman arrives to give evidence at the impeachment hearings into the conduct of Donald Trump (EPA)

Mr Vindman did not have dealings with Hickman in relation to his work during the exercise, the person said, and was not reprimanded for it.

Peter Zwack, a retired brigadier general who was Mr Vindman’s commanding officer during the joint exercise, said he was sceptical of Mr Hickman’s account.

“If there was something egregious that occurred, believe me, we would have had our ears rapped in Moscow,” said Mr Zwack, who served as the United States’ senior defence official and attache to Russia.

“The bottom line is, where there are Russians in an exercise in and among our units and people, we have an attache that coordinates with them,” the general said. “It’s all just a part of an attaches' job.”

Attaches are expected to overtly collect information on what is happening in the country in which they are posted, as well as collect information from unsuspecting foreign officials through casual conversation. The allegations made by Hickman may simply describe Vindman playing his assigned role.