The White House’s trenchant declaration to House impeachment investigators last week was unequivocal: no more witnesses or documents for a “totally compromised kangaroo court”.

But just a week later, it has become clear that Donald Trump’s attempts to stonewall the Democrat-led inquiry that has imperilled his presidency and ensnared much of his inner circle are crumbling.

One by one, a parade of Trump administration career diplomats and senior officials has offered a cascade of revelations.

Those accounts have corroborated and expanded upon key aspects of the whistleblower complaint that spawned the impeachment inquiry into whether the president abused his power to enlist Ukraine to help him in the 2020 presidential election.

The latest disclosures came on Wednesday, when a former top aide to secretary of state Mike Pompeo offered an inside account of what he said was a demoralised State Department, where career diplomats were sidelined and others apparently were pressed to use their posts “to advance domestic political objectives”.

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

In six hours of voluntary testimony, the former aide, Michael McKinley, told impeachment investigators that he quit his post as Mr Pompeo’s senior adviser amid mounting frustrations over the Trump administration’s treatment of diplomats and its failure to support them in the face of the impeachment inquiry, according to a copy of his opening remarks.

On Thursday, Democrats are set to hear from Gordon D Sondland, the US ambassador to the European Union, a central figure in the president’s pressure campaign on Ukraine.

He is expected to testify that he learned that Mr Trump did not intend to invite Volodymyr Zelenskiy to a meeting in the Oval Office until the Ukrainian president pledged to open an investigation that could benefit Mr Trump’s political fortunes — bolstering a central allegation in the inquiry that the president steered foreign policy for political gain.

And Democratic lawmakers have directed William B Taylor Jr, one of the top American diplomats in Ukraine, to appear before their committees next Tuesday, according to an official familiar with the investigation.

Text messages produced as part of the inquiry suggest that Mr Taylor was deeply uneasy about what he saw as an effort by Trump aides to use a $391m (£305m) package of security assistance as leverage over Ukraine for political favours, calling the notion “crazy”.

All three are examples of what can happen when congress secures cooperation from government witnesses in a rapidly moving investigation aimed at the president.

The White House has had more success blocking the release of documents tied to the case. But the president and his lawyers had hoped to use the power of his office to muzzle current and former diplomats and White House aides, arguing in presidential tweets and a lengthy letter to Democratic lawmakers on 8 October that their subpoenas are invalid and unenforceable.

Hunter Biden calls Donald Trump Jr Prince Humperdinck from Princess Bride and his dad the Cheshire Cat

“President Trump cannot permit his administration to participate in this partisan inquiry under these circumstances,” wrote Pat Cipollone, the White House counsel.

And yet the president has been unable to prevent it.

Just since Mr Trump declared war on the impeachment effort, three current and former senior State Department officials and a former top White House aide have testified for nearly 36 total hours, delivering to lawmakers a consistent narrative of how they were effectively pushed aside by allies of the president operating outside America’s usual foreign policy channels.

“It’s partly because this shadow foreign policy that the president was running was so deeply offensive to people in his own administration who took pride in overseeing a professionally run and arguably exemplary policy in support of Ukraine,” said congressman Tom Malinowski, a former State Department official involved in the inquiry.

Referring to the president’s personal lawyer, he added: “And then to see the official policy undermined by this clownishly corrupt effort led by Rudy Giuliani on behalf of the president was just more than many people apparently could bear.”

Republicans who control the Senate view the fast-building case as serious enough to begin preparing for the trial in their chamber that would follow impeachment by the House.

Senator Mitch McConnell, the majority leader, briefed fellow lawmakers over lunch Wednesday about how a trial would work, expressing his hope of conducting it speedily and completing it by the end of the year, people familiar with his remarks said.

Facing accusations of secrecy from Republicans, congressman Adam B Schiff, chairman of the Intelligence Committee, informed colleagues on Wednesday that he planned to open the inquiry to the public soon.

He wrote that he planned to release transcripts of all the interviews as the investigation proceeded and pledged to soon hold public hearings “so that the full Congress and the American people can hear their testimony firsthand”.

For Mr Trump, who is famous for demanding fierce loyalty from those around him, the daily — or even hourly — crush of damaging headlines is an infuriating departure from previous successes in controlling disclosures to congress from people in his orbit.

During the congressional investigation into Russia’s election meddling, the US president blocked a deposition of Donald F McGahn II, his former White House counsel, and dramatically limited testimony from some of his closest aides, including Hope Hicks, the former White House communications director, and Corey Lewandowski, his former campaign manager.

Trump impeachment: Nancy Pelosi decides not to call vote authorising probe

But this is different. Many administration officials targeted for depositions by Democrats are diplomatic veterans who have expressed anger and frustration about what they described as the hijacking of US foreign policy. They have no particular loyalty to mr Trump nor are they subject to the same presidential powers to block them from testifying.

So they have turned up at the secure suite of the House Intelligence Committee on Capitol Hill, disappearing behind doors with a red “RESTRICTED AREA” sign to tell their stories.

Under alternating hour-long question-and-answer sessions by Democratic and Republican staff lawyers, Marie Yovanovitch, the former ambassador to Ukraine, said she had been ousted at Mr Trump’s direction on the basis of “unfounded and false claims”.

Fiona Hill, a former National Security Council aide, said John Bolton, then the national security adviser, was so alarmed by the activities of Mr Giuliani, Mr Sondland and others that he instructed her to alert White House lawyers.

She said she reported Mr Sondland to intelligence officials as a possible national security risk as well.

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Mr McKinley told investigators on Wednesday that State Department officials were discouraging people from testifying and were not supporting diplomats who had received subpoenas and requests to appear before the House, according to a person familiar with his testimony.

Mr Trump’s allies on Capitol Hill expressed frustration this week about the depositions, saying White House lawyers should be present and accusing Democrats of selectively leaking from the testimony. Others were simply baffled by the cooperation of the witnesses.

“I really don’t understand it,” said congressman Chris Stewart, a member of the Intelligence Committee. “I can’t wrap my head around why some and why not others.”

Mr Trump’s lawyers have had more success in blocking access to emails, text messages, memos and other documents in the government’s possession.

The administration has rejected Democratic subpoenas or requests for documents at the Office of Management and Budget, the State Department, the Defence Department and the office of vice president Mike Pence.

Mr Giuliani has also said he will ignore a subpoena for his records, citing the White House’s stance.

Democrats have said the refusal to hand over documents will be considered obstruction of congress and may be added to the impeachment charges brought against the president.