Washington (CNN) It may be President Donald Trump in the sights of congressional investigators pursuing impeachment. But every day it becomes clearer he's not acting alone.

The circle of men who surround the President have shown ample willingness to fuel and fulfill his drive to meld politics and foreign policy. They have mounted a staunch defense not just of him but of their own behavior in the wake of a whistleblower complaint about a July call between Trump and Ukrainian President Volodymyr Zelensky.

What exactly they knew about Trump's efforts to solicit dirt on political rivals is still becoming clear. But there is little evidence of pushback among those closest to the President. Instead, there are signs Cabinet members and top allies actively pursued leads on conspiracy theories and political muckraking.

Working for Trump has routinely amounted to a loyalty test for aides, who are often asked to put aside political and ethical norms to carry out the President's orders. Underlings who fail to comply are rare, and those who do quickly fall from favor.

Now, the limits of those loyalties will be tested as Trump faces impeachment in the House of Representatives and accusations he's abused his power. As the inquiry speeds ahead, the decisions and actions made by the President's inner-circle are coming into sharper focus.

Rudy Giuliani

Rudy Giuliani, the President's private lawyer, has been front and center to the Ukraine controversy, taking a high-profile role on the cable news circuit in recent weeks.

Even before Zelensky took office, Giuliani made known he was looking to set up a meeting to discuss an investigation into Burisma, the natural gas company where Biden's son Hunter had served on the board of directors. There is no evidence of wrongdoing by either Joe Biden or his son.

Giuliani met with a lawyer for Zelensky by phone and in person over the summer. Zelensky said Tuesday he never met or spoke to Giuliani by phone or in person. Giuliani was critical in stoking the President's interest in Ukraine.

The former New York City mayor was referenced repeatedly during the phone call between Trump and Zelensky, and has admitted that he asked Ukraine to investigate the Bidens, including during an interview with CNN's Chris Cuomo.

The whistleblower's complaint called Giuliani's role as both the President's personal lawyer and an informal diplomat circumventing traditional channels into question. The whistleblower said they heard that two State Department officials intervened with Giuliani in an effort to "contain the damage" he was doing to national security. The complaint also said US diplomats worked with the new Ukrainian leaders to help them navigate the strange situation, where they juggled outreach from Giuliani with US diplomacy coming through official channels.

Giuliani was subpoenaed by House Democrats Monday in their impeachment inquiry. Though he has so far given conflicting answers as to whether he will comply, he has until October 15 to turn over documents relating to Ukraine.

Giuliani could seek to shield himself behind attorney-client privilege and the White House could potentially try to invoke executive privilege given its past such expansive claims. But it is not clear how such claims would hold up in court -- since Giuliani has spilled plenty of detail about his dealings with Ukraine in freewheeling media appearances that may constitute a waiving of privileges.

William Barr

Along with Giuliani, Trump also asked Zelensky to work with Attorney General William Barr to investigate the Bidens, the White House transcript of the Ukraine call shows. Barr was also among the group of Trump insiders encouraging the President to release the details of the call.

Barr's suspected involvement has led Democrats to call on the attorney general to provide more information to Congress, and House Judiciary Chairman Jerry Nadler went so far as to call on Barr to recuse himself from matters related to the call.

House Intelligence Committee Chairman Adam Schiff sent a letter to Barr demanding information and records regarding the handling of the whistleblower complaint, which the Office of the Director of National Intelligence initially did not give to Congress, and Senate Democrats have asked Senate Judiciary Committee Chairman Lindsey Graham to have Barr testify.

The Justice Department said in a statement that Barr "was first notified of the President's conversation with Zelensky several weeks after the call took place, when the department learned of a potential referral."

"The President has not spoken with the Attorney General about having Ukraine investigate anything relating to former Vice President Biden or his son," the statement continued.

This isn't the only Trump call with a foreign leader that Barr is connected to.

Trump pressed Australia's Prime Minister Scott Morrison during a recent phone call to help Barr with his review of the origins of the Russia probe, according to an official familiar with the call.

An official briefed on the matter said the attorney general has asked the President to request the help of several countries, including Australia, with the review of the early stages of the Russia investigation.

The call happened with Barr's knowledge and at his suggestion, says the official.

The Washington Post reported Monday that Barr has also held private meetings with foreign intelligence officials overseas seeking their help in the Justice Department inquiry into the origins of the Mueller probe, according to people familiar with the matter.

Mike Pence

Always careful to avoid both breaking with Trump and embroiling himself in the President's various controversies, Pence has nonetheless found himself pulled into the impeachment fray. His involvement began in the spring, when his tentative plans to attend the newly elected Ukrainian President's inauguration were scrapped by Trump himself.

Another twist of scheduling led to Pence meeting Zelensky last month in Poland after the President scrapped a planned trip and sent his number two instead. By that point, an intelligence whistleblower had already filed a complaint centered on Trump's behavior toward Ukraine.

During his trip, Pence was questioned by reporters on whether the issue involving Biden's son arose in his meeting. He said it did not -- but quickly turned to the issue of corruption. The comment came after the Trump administration and Giuliani initially sought to spin Trump's request to Zelensky about Biden.

"As President Trump had me make clear, we have great concerns about issues of corruption. And, fortunately, President Zelensky was elected decisively on an anti-corruption message," Pence said, adding later: "To invest additional taxpayer money in Ukraine, the President wants to be assured that those resources are truly making their way to the kind of investments that will contribute to security and stability in Ukraine. And that's an expectation the American people have and the President has expressed very clearly."

Amid the furor over Trump's interactions with Zelensky, Pence's conversations largely went unnoticed -- until the President himself raised during a news conference last week.

"Ask for VP Pence's conversation, because he had a couple conversations also," Trump told reporters. So far, Pence's office hasn't released transcripts of his phone conversations with Zelensky.

Mike Pompeo

Beyond his role as the nation's chief diplomat, Secretary of State Mike Pompeo became further ensnared in the controversy Monday when it was reported he was on the July 25 with Zelensky call himself, according to a source familiar with the call. His role is under further scrutiny in light of the whistleblower's complaint that the State Department was working to minimize fallout from Giuliani's backchannel actions.

Pompeo was asked about the whistleblower complaint last week while in New York for the United Nations General Assembly and said at the time he had not yet read it in full. When asked if he or his staff acted improperly Pompeo did say that, to the best of his knowledge, "each of the actions that were undertaken by State Department officials was entirely appropriate." He offered a similar response during an ABC News interview last month when questioned about the complaint. "You just gave me a report about a (intelligence community) whistleblower complaint, none of which I've seen," Pompeo said at the time

Pompeo was one of the officials who publicly urged against the release of the transcript, saying in that same ABC News interview in the days before the transcript was released, "there's no evidence that would be appropriate here at this point."

"We don't release transcripts very often. It's the rare case," Pompeo said. "Those are private conversations between world leaders, and it wouldn't be appropriate to do so except in the most extreme circumstances."

Democrats have subpoenaed Pompeo over his failure to produce documents related to Ukraine. They also informed Pompeo they have scheduled depositions for five State Department officials who have been mentioned in relation to the inquiry -- Ambassador Marie "Masha" Yovanovitch, Ambassador Kurt Volker, Deputy Assistant Secretary George Kent, Counselor T. Ulrich Brechbuhl and Ambassador Gordon Sondland.

On Tuesday, Pompeo accused House Democrats of intimidating and bullying those officials. One of those officials, Marie "Masha" Yovanovitch, was referenced during Trump's call. Trump disparaged the former US Ambassador to Ukraine during his conversation with Zelensky, calling her "bad news," in what was a stunning breach of norms, former officials say. The State Department has not responded to CNN's request for comment, and Pompeo has not defended her publicly.

"I'm concerned with aspects of the Committee's request that can be understood only as an attempt to intimidate, bully, & treat improperly the distinguished professionals of the Department of State, including several career (foreign service officers)," he tweeted.

In a second tweet he added, "Let me be clear: I will not tolerate such tactics, and I will use all means at my disposal to prevent and expose any attempts to intimidate the dedicated professionals whom I am proud to lead and serve alongside at the Department of State."

This week, Pompeo is traveling in Italy, the Holy See, Montenegro, North Macedonia and Greece, for what a senior State Department official described as an opportunity to "(affirm) and (endure) the strength of our alliance and partnerships" through strengthening economic and security ties and "confirming our commitment to the advancement of religious freedom globally."

Lindsey Graham

Graham, a staunch Trump ally, was also among those urging the President release the transcript of the Ukraine call.

Graham has called Trump's behavior during the call "ethical" and dismissed suggestions that the call rose to the level of launching an impeachment inquiry.

"Impeachment over this? What a nothing (non-quid pro quo) burger. Democrats have lost their minds when it comes to President," Graham tweeted last week.

The reaction stands in stark contrast to when Graham was on the House Judiciary Committee in the late 1990s. He served as one of 13 "managers" -- a prosecutor-like role -- during then-President Bill Clinton's impeachment trial. At the time, Graham declared that, "you don't even have to be convicted of a crime to lose your job in this constitutional republic if this body determines that your conduct as a public official is clearly out of bounds in your role."

"Impeachment is not about punishment. Impeachment is about cleansing the office. Impeachment is about restoring honor and integrity to the office," he added.

Graham's defense of the Ukraine call landed him in hot water with the Intelligence Community Inspector General, Michael Atkinson, who elevated the whistleblower report to Congress when the acting Director of National Intelligence would not.

Atkinson disputed what Trump and surrogates, including Graham, have said about the whistleblower lacking firsthand knowledge. In a rare statement, Atkinson said the whistleblower had "direct knowledge of certain alleged conduct."

Graham also holds a unique seat to power as a member of Senate committees central to the call.

As the Senate Judiciary Committee chairman, Graham has been asked by Senate Democrats to hold hearings over the call. Democrats said in a letter that they'd like to hear from Barr, White House counsel Pat Cipollone, and the Justice Department Inspector General, among others.

And as a former member of the Senate Armed Services Committee and current member of the Senate Foreign Relations Committee, Graham also bore witness to the delay of Ukraine obtaining the US military aid Congress had approved -- the aid which the whistleblower indicated was held up by the White House. Still, Graham has maintained that there is no connection between the money being held up and the President trying to get dirt on his potential political opponents.

"I called the Pentagon. The Pentagon said that they were worried about the new administration, they were doing their due diligence, they were worried about corruption, they were worried about military aid. They wanted to figure out what was what. I said, 'Fine, just figure it out,'" Graham said, adding that it wasn't unusual for Trump not to be keen on foreign aid

Mick Mulvaney

The President asked acting White House chief of staff Mick Mulvaney to put the millions of dollars in military aid to Ukraine on hold -- one week before the Ukraine call, two senior administration officials told CNN.

Trump, who was in the middle of a broad review of foreign aid programs when he singled out Ukraine specifically this summer, was primarily concerned with "corruption" in Ukraine and Europe shouldering more of the financial burden for supporting Ukraine's defense, according to one of the officials.

While the White House counsel's office had been scrambling to address the whistleblower's concerns since July, Mulvaney was not informed of the whistleblower concerns until a few days before the Ukraine call transcript was released, two sources familiar with the situation told CNN.

Now, Mulvaney is on shaky ground in the wake of a bad week for Trump, according to multiple sources with knowledge of discussions surrounding the whistleblower fallout.

Mulvaney has also soured to the idea of an impeachment war room, according to a White House official.