US officials were rocked by the revelation this week that a "credible" whistleblower complaint of "urgent concern" involved multiple acts by President Donald Trump, including a phone call with a foreign leader and a "promise" he made to the person.

Insider asked half a dozen current and former officials across different intelligence agencies whether they knew of any other case in which someone within the intelligence community blew the whistle on the president. All said no.

The Office of the Director of National Intelligence is withholding the complaint from Congress.

"This is a really big deal," said one former top lawyer at the CIA and National Security Agency. "They must have known that withholding this complaint would eventually attract attention from the public, and they did it anyway. That suggests that what they're worried about in the complaint is far worse."

The unprecedented nature of the situation prompted a former CIA official to tell Insider it's "equivalent to an imminent threat" in the intelligence community, adding: "DEFCON 1."

"To be in this line of work and then to file a formal complaint against the sitting president and the commander in chief based on something he said — something that was so deeply alarming — that's an impossible situation to be in," one FBI agent who works in counterintelligence told Insider.

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Recent revelations from The Washington Post about the contents of a whistleblower complaint filed within the intelligence community have rocked Washington and thrust the US into uncharted territory.

The Post reported that part of the complaint involved President Donald Trump's communication with a foreign leader and a "promise" Trump made during a phone call with that person. It's unclear who the leader is or what the substance of the conversation was. The New York Times later reported that the complaint covered multiple acts by Trump that went beyond any single discussion with a foreign leader.

Insider asked half a dozen current and former officials across different intelligence agencies whether they were aware of any other case in which someone within the intelligence community blew the whistle on the president. All of them said no.

"I can't think of any other scenario like this," James Baker, the former general counsel of the FBI, told Insider. He cautioned that many details about the complaint were still unknown but added: "Having said that, I would take this matter very seriously."

According to the House Intelligence Committee chairman, Rep. Adam Schiff of California, the whistleblower filed the complaint with the intelligence community inspector general on August 12. The inspector general reviewed the information and found that the complaint was credible and a matter of "urgent concern" and conveyed that finding to the Office of the Director of National Intelligence.

But instead of forwarding the complaint to the congressional intelligence committees — as is mandated by federal law — the acting director of national intelligence, Joseph Maguire, consulted the Justice Department and determined he was not required to turn over the complaint to Congress because it involved conduct by someone outside the intelligence community and involved "confidential and potentially privileged communications."

The White House did not immediately return a request for comment Thursday.

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Robert Deitz, a former top lawyer at the CIA and the National Security Agency, told Insider he didn't think the director of national intelligence's rationale held much water — in part because the commander in chief leads the intelligence community.

He added that it's more likely Maguire's refusal to turn over the complaint was rooted in fear of political blowback.

"I can't think of any lawful ground for doing what he's doing," Deitz said. "They must have known that withholding this complaint would eventually attract attention from the public, and they did it anyway. That suggests that what they're worried about in the complaint is far worse."

"This is a really big deal," Deitz added. "And for the IC IG to determine that this is credible and urgent, that's a horse of a different color. That assessment matters."

The seemingly unprecedented nature of the situation, moreover, prompted one former CIA official to tell Insider it's "equivalent to an imminent threat" in the intelligence community.

"DEFCON 1," the former official added.

President Donald Trump tours a section of the southern border wall, Wednesday, Sept. 18, 2019, in Otay Mesa, Calif. (AP Photo/Evan Vucci) Associated Press

'It must involve illegality or wrongdoing of some sort'

Michael Atkinson, the intelligence community inspector general, testified before the House Intelligence Committee in a closed session Thursday but refused to go into detail about the content of the complaint. Maguire is expected to appear before the panel in an open session next week and is also unlikely to reveal more about the matter.

Edward Price, a senior director of the National Security Council under President Barack Obama, told Insider that according to the relevant statute, the whistleblower complaint couldn't center on a policy disagreement to be deemed credible and urgent.

"It must involve illegality or wrongdoing of some sort," Price said. And because the inspector general determined that the complaint fit that criterion, it suggests the whistleblower knows something "highly troubling," he added.

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The Post reported that Trump interacted with five foreign leaders in the five weeks leading up to when the whistleblower filed the complaint. One of those interactions, with Russian President Vladimir Putin on July 31, involved a phone call.

The White House's readout of the call said Trump — who initiated the conversation — discussed the possibility of American assistance to wildfires that were ravaging Siberia at the time.

The Kremlin's readout of the call added an important nugget: that Putin viewed Trump's offer as a sign that "fully fledged bilateral relations" between the US and Russia "could be restored in the future."

One possibility, Price said, is that "Trump made a promise to Putin to normalize relations — as the Kremlin readout suggests was the case — in return for something that benefitted Trump personally."

"In other words, this could've been a quid pro quo in which the quid was a change in US policy to benefit Moscow, while the quo was something in return for Trump himself," Price added.

Russian President Vladimir Putin. Reuters

'This person didn't do this lightly or casually'

Current and former officials also said the way the complaint was filed spoke volumes.

One FBI agent who works in counterintelligence told Insider they couldn't "overstate how difficult it must have been" for the whistleblower "to take such an enormous step."

The person added: "To be in this line of work and then to file a formal complaint against the sitting president and the commander in chief based on something he said — something that was so deeply alarming — that's an impossible situation to be in."

Deitz echoed that view.

"This isn't somebody who immediately called [the media] the way people like Edward Snowden did," he said. "This is a person who's operating absolutely correctly, through legal channels, and isn't concerned about gaining publicity and attention but is concerned about the safety of the country. This person didn't do this lightly or casually."

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The whistleblower's complaint about the president and the public firestorm surrounding it are also likely to put more strain on Trump's already tense relationship with the spy agencies he leads.

Trump has repeatedly shown an unwillingness to accept findings that don't align with his own views. Indeed, he publicly sided with Russia over the intel community on the issue of Russian election interference, and he said his own intelligence chiefs were "passive and naive" because they contradicted him on issues like Iran and North Korea.

Moreover, the president is reluctant to rely on some of the most basic intelligence-gathering techniques the US has employed for decades, like the use of foreign spies, who are crucial to providing information about hostile countries.

Though the president has a wide-reaching ability to declassify information, Trump has been accused of mishandling sensitive information in the past. In 2017, he revealed classified secrets provided to the US by Israeli intelligence to two Russian officials in an Oval Office meeting. And late last month, he tweeted out a photo of an Iranian launch pad that appeared to be taken by a classified US spy satellite.

"Many presidents don't have an understanding of the intelligence business, and that's OK because that's what you have advisers for," Deitz said. "What's unique about Trump is that he doesn't seem to care because he's so sure his instincts are superior. And that scares the hell out of people in the intelligence community."

"The president depends so heavily on high-quality intelligence analysis that it's really not in his or the country's interest for him not to have an excellent working relationship with the intel community," Baker said. "This could potentially affect what intel leaders share, and what he shares with them, too."

Deitz agreed: "I'd be surprised if, after this whistleblower complaint, they continue providing him with the crown jewels, if they were even doing that in the first place."