President Donald Trump retweeted a post naming the alleged whistleblower who filed the complaint that became the catalyst for the congressional inquiry that resulted in his impeachment by the House of Representatives.

On Friday night, Mr Trump shared a Twitter post from @surfermom77, who describes herself as “100 per cent Trump supporter”, with his 68 million followers. That tweet prominently named the alleged whistleblower and suggested that he had committed perjury.

By Saturday morning, the post did not appear on Mr Trump's timeline, though it was visible to certain users and via direct link. On Saturday evening, Twitter acknowledged that a technical glitch made Mr Trump's retweet appear visible to some users but not others.

“Due to an outage with one of our systems, tweets on account profiles were visible to some, but not others,” Twitter said in a statement. “We're still working on fixing this and apologise for any confusion.”

Twitter said the discrepancy – with the tweet appearing for some and not others – was the result of a system error that affected tweets from millions of users, including the president.

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

For months, Mr Trump has threatened to disclose the identity of the whistleblower, complaining that he should be able to face his accuser. In the past few days, he has inched closer to doing so. On Thursday night, the president retweeted a link to a Washington Examiner story that used the name.

The alleged whistleblower has also been named in other conservative media, including Breitbart News. He was named by a contributor on Fox News, and Donald Trump Jr has tweeted the name.

The White House did not respond to a request for comment.

The whistleblower's identity has been kept secret because of whistleblower protection laws, which exist to shield those who come forward with allegations of wrongdoing by the government. Whistleblower advocates say this anonymity is important, because it protects those who speak up from retaliation and encourages others to come forward.

The Washington Post has chosen not to publish the name. Vice president for communications Kris Coratti said The Post “has long respected the right of whistleblowers to report wrongdoing in confidence, which protects them against retaliation. We also withhold identities or other facts when we believe that publication would put an individual at risk. Both of those considerations apply in this case”.

Mr Trump and his allies claim the law does not forbid disclosing the identity of the whistleblower. Federal laws offer only limited protection for those in the intelligence community who report wrongdoing, and those in the intelligence community have even fewer protections than their counterparts in other agencies.

The 1998 Intelligence Community Whistleblower Protection Act did not detail any protections for whistleblowers from retaliation – instead merely describing the process to make a complaint.

Whistleblower attorney Bradley Moss told the The Post in September that the law does not apply to members of Congress who might disclose the whistleblower's name. “This is all very, very fragile, and a lot of the protections that we understand to exist are based more on courtesy and custom than anything written down in law,” Mr Moss said.

Mr Trump has been baiting the whistleblower's name even before Nancy Pelosi announced a trial would go ahead (Getty)

Mr Moss is the law partner of Mark Zaid, one of the whistleblower's attorneys, though he has had no involvement in that case.

Attorney Stephen Kohn, an expert in whistleblower protection laws, said this circumstance is unprecedented given the president's unique duty to protect the confidentiality of intelligence agency whistleblowers.

In the whistleblower protection act that covers the intelligence community, Congress gave the president enforcement authority to protect the whistleblower because of the sensitivity of what that person could be revealing.

“The paradox is that it was the president's duty to protect this person,” Mr Kohn said. “It's inconceivable that he not only doesn't do it, but violates it.”

The whistleblower, who works for the CIA, filed an official complaint that, among other concerns, pointed to a 25 July phone conversation in which Mr Trump asked Ukrainian president Volodymyr Zelensky to investigate former vice president Joe Biden, a Democratic presidential candidate.

After several months of investigation, the House voted 18 December to impeach Trump on charges of abuse of power and obstruction of Congress. The senate will hold a trial – where the Republican majority is expected to acquit him – in early 2020, once House speaker Nancy Pelosi transfers the articles of impeachment.

A complaint about a 25 July phonecall from Mr Trump asking Ukraine to investigate Joe Biden triggered the inquiry (Getty)

Congressional Republicans have demanded the whistleblower testify as part of the impeachment probe. Democrats have countered that such testimony is unnecessary because other witnesses have corroborated and expanded on the original complaint, which was based on secondhand information.

The president has repeatedly disparaged the whistleblower, though never by name, in tweets, interviews and rally speeches. In late September, Mr Trump accused the whistleblower's sources of being “close to a spy”, adding, “you know what we used to do in the old days when we were smart? Right? With spies and treason, right? We used to handle them a little differently than we do now” .

In early November, the whistleblower's attorney sent White House counsel Pat Cipollone a cease-and-desist letter, demanding the president stop denigrating the whistleblower.

“I am writing out of deep concern that your client, the president of the United States, is engaging in rhetoric and activity that places my client, the intelligence community whistleblower, and their family in physical danger,” wrote attorney Andrew Bakaj. “I am writing to respectfully request that you counsel your client on the legal and ethical peril in which he is placing himself should anyone be physically harmed as a result of his, or his surrogates', behaviour.”

The whistleblower, who is reportedly still at his job, is driven to and from work by armed security officers when threats are elevated. Threats against him seem to spike whenever Mr Trump tweets about him, The Post has previously reported.

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The Twitter feed for @surfermom77, who identifies herself as “Sophia” on the social media site, is a daily stream of pro-Trump and anti-Democrat memes and propaganda. In 2016, the account shared the false conspiracy theory that former president Barack Obama was a Muslim.

In the days after Christmas, Mr Trump retweeted more than a dozen posts from users affiliated with QAnon, the conspiracy theory that there is a “deep state” secretly plotting to take down Mr Trump. The FBI has identified QAnon as a potential domestic terrorism threat.

On Saturday morning, former solicitor general Neal Katyal, a frequent Trump critic, reacted to Mr Trump's retweet, writing on Twitter: “Who would want to live in a country where its leader could just name the identity of a whistleblower and invite retaliation against him? Despicable, un-American, and @MittRomney your country (and your Party) needs you now.”

Former Democratic senator Claire McCaskill (Missouri), who sponsored whistleblower protection legislation in the senate, singled out another Republican on Saturday, tweeting at senator Charles Grassley, who co-founded the Senate Whistleblower Protection Caucus and has authored and co-authored many of the nation's whistleblower protection laws. “@ChuckGrassley where the hell are you?” Ms McCaskill tweeted. “We worked hard on whistleblower protections. I thought your desire to protect and defend whistleblowers was in your bones. Was I wrong? What happened to you?”

Representatives for Mr Grassley and Mr Romney did not immediately respond to a request for comment.