The White House’s disjointed response to Democrats’ impeachment inquiry has been fuelled by a fierce West Wing battle between two of Donald Trump’s top advisers and the outcome of the messy skirmish could be on full display this week, according to White House and congressional officials.

Acting chief of staff Mick Mulvaney has urged aides not to comply with the inquiry and blocked any cooperation with congressional Democrats.

Top political aides at the Office of Management and Budget, which Mr Mulvaney once led, have fallen in line with his defiant stance, the officials said, speaking on the condition of anonymity so they could to talk freely about the behind the scenes developments.

Mr Mulvaney’s office blames White House counsel Pat Cipollone for not doing more to stop other government officials from participating in the impeachment inquiry, as a number of State Department officials, diplomats, and an aide to vice president Mike Pence, have given sworn testimony to Congress.

Mr Cipollone, meanwhile, has fumed that Mr Mulvaney has only made matters worse with his 17 October news conference, when he publicly acknowledged a quid pro quo, essentially confirming Democrats’ accusations in front of television cameras and reporters.

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

Mr Cipollone did not want Mr Mulvaney to hold the news conference, a message that was passed along to the acting chief of staff’s office, according to two senior Trump advisers, who spoke on the condition of anonymity.

An aide for Mr Mulvaney said a team of White House lawyers prepared him for the news conference and never said he should not do it.

Neither Mr Mulvaney nor Mr Cipollone has broad experience navigating a White House through such a tumultuous period.

But their actions have contributed to the White House’s increasingly tenuous response to the impeachment inquiry, in which public hearings are set to begin later this week in the House.

Despite the high stakes, the White House moved slowly to hire a staff specifically dedicated to working on the impeachment issue, a concern that was expressed to the White House by multiple Republican senators, Capitol Hill aides said.

“This will be the toughest political fight this White House has faced. They need to be sure they are totally-focused, and that all their fire is pointed outward – not at each other,” said Michael Steel, a Republican strategist who was a top aide to former House speaker John Boehner.

Complicating matters, on Friday, the same day he defied a congressional subpoena to testify, Mr Mulvaney sought to join a separation-of-powers lawsuit filed against Mr Trump and the House leadership by a one-time deputy to former national security adviser John Bolton.

The move infuriated Bolton allies, The Washington Post has reported, partly because Mr Bolton and other national security aides viewed Mr Mulvaney as a key architect in pressuring Ukraine to launch political investigations on behalf of Mr Trump.

Mr Mulvaney’s move to join the lawsuit baffled several administration officials, people familiar with the matter said.

The lawsuit could have provided a legal basis for Mr Mulvaney’s refusal to testify in the impeachment inquiry, but he withdrew, saying he will file his own suit to ask the courts to decide whether senior Trump administration officials must testify in the impeachment inquiry.

The Office of Management and Budget (OMB) has served as Mr Mulvaney’s biggest bulwark, because it played a key role in blocking nearly $400m (£312m) in security aide to Ukraine over the summer.

The OMB is led by a close Mulvaney ally, acting director Russell Vought, who has refused to cooperate with the impeachment inquiry, as have other political appointees at the agency.

But the increasingly political nature of the OMB has rattled a number of high-level career staffers, and several have resigned in the past year, including one who announced his departure in the midst of the turmoil this summer.

Acting White House chief of staff Mick Mulvaney (L) and White House counsel Pat Cipollone (Alex Wong/Getty Images)

Employees at the normally under-the-radar budget agency watched in dismay as political appointees at the OMB took the highly unusual step of overruling the concerns of career staff to hold up the Ukraine military aid, according to multiple former agency officials who remain in touch with current employees and spoke on the condition of anonymity to protect career staffers.

“Everyone was freaked out because it so violated the norms of OMB,” said one former longtime career employee, speaking on condition of anonymity to discuss private conversations.

The impeachment inquiry now threatens to ensnare career staffers at OMB, one of whom, Mark Sandy, was called to testify on Friday but failed to appear.

A series of State Department and national security witnesses have told impeachment investigators that the aid was held up as part of a quid pro quo to get Ukraine to announce investigations, including of Mr Trump’s Democratic rival Joe Biden, but OMB staffers could fill in key details of what took place.

The White House denied the existence of any internal tensions.

“We are one team and we work well together. The palace intrigue stories are false and they need to stop,” White House press secretary Stephanie Grisham said in an email.

But Mr Trump has complained about his legal team to White House officials and advisers in recent weeks, saying they need to be more aggressive and defend him more.

Mr Cipollone released a letter from Mr Trump early last month saying the White House would not be cooperating with the impeachment inquiry. But a senior administration official said Mr Cipollone since then has failed to do more to keep members of the administration in line.

“Those who have aligned with the president and followed the president’s instincts on not to cooperate have been successful and been that firewall,” said this official, who spoke on the condition of anonymity to discuss internal deliberations.

Mr Cipollone, this person said, “has been pretty weak in ensuring people are on lockdown”.

At the same time, Mr Trump has been complaining about Mulvaney, blaming him for his political troubles, and has toyed with the idea of replacing him, two officials said.

Trump's Ukraine call not a problem because he speaks like that 'all the time', says Rep Mac Thornberry

Another dispute between the Mulvaney and Cipollone camps emerged over the potential hiring of former congressman Trey Gowdy to be part Mr Trump’s team defending against impeachment.

Mr Trump was looking for outspoken supporters and Mr Mulvaney advocated for hiring his former House colleague and longtime friend Mr Gowdy, a former federal prosecutor-turned-Fox News personality.

But Mr Cipollone was opposed. And ultimately the Gowdy boomlet collapsed within a period of days last month as White House officials said federal lobbying rules could prevent him from starting until January.

Some administration officials complain that Mr Cipollone has not kept Mr Mulvaney and other White House offices in the loop on key decisions.

Mr Cipollone’s office released the transcript of the president’s 25 July call with his Ukrainian counterpart – a move that Mr Mulvaney opposed, administration officials said.

Neither the acting chief of staff nor some members of the White House press office knew ahead of time that was going to happen, the officials said.

Some Hill Republicans were not pleased and have accused Mr Cipollone of being territorial behind the scenes.

They wanted Mr Gowdy, who led the party's investigation of the Benghazi terrorist attack on the US consulate in Libya, to lead the cross-examination for Mr Trump in the Senate – a role Mr Cipollone is said to want for himself.

“Each wants to be in charge of impeachment,” one Senate Republican aide said of the Mulvaney-Cipollone fight. “Cipollone seems more like he’s protecting his turf than anything else ... He doesn’t want any competition.” The aide spoke on the condition of anonymity to freely describe private concerns.

Tensions between the two camps were inflamed when Mr Mulvaney gave a 17 October briefing to White House reporters and appeared to acknowledge the president sought to withhold the US aid to Ukraine as part of a quid pro quo.

Mr Mulvaney said the administration did not release the security assistance to the country because the president wanted Ukraine to first agree to an investigation into corruption, and a discredited theory that evidence of Russia’s interference in the 2016 election had been fabricated.

Mr Mulvaney later issued a statement insisting that he had not confirmed a quid pro quo and that reporters had misinterpreted his words, which were televised.

Impeachment hearings come at the very time Capitol Hill usually tends to its mound of unfinished business (AP Photo/J. Scott Applewhite)

The divisions within the administration, at a time when it should be presenting a united front against House Democrats, are serious enough that they have caught the attention of Senate Republicans, who are concerned that the administration is not properly prepared for a Senate impeachment trial that could start in January.

The House is expected to pass articles of impeachment against Mr Trump as soon as December, triggering a trial in the Senate.

“This impeachment trial is going to be here before the White House knows it and they’re not even remotely prepared for it,” said the Senate GOP aide.

“What they need desperately is leadership to get ready, but until Mulvaney and Cipollone put aside their petty squabbles and start working together all they’ll have is tweets.”

This aide said that Republican senators have been concerned that the White House was moving too slowly to hire staff specifically dedicated to working on the impeachment issue as the inquiry moves into its public phase. Multiple senators made this concern known to the White House, the aide said.

Their concerns were finally alleviated last week with news that Pam Bondi, the former attorney general of Florida, and Tony Sayegh, a former Treasury Department spokesman, would join the administration to work on impeachment-related messaging and other issues.

“I think Pam Bondi will be very helpful,” said Lindsey Graham, adding that the Senate is unlikely to remove the president. “Things are better now, I think. Pam will do a good job. They still need to build their legal team out some.”