FBI officials were "rattled" and "blindsided" by President Donald Trump's calls for Ukraine to manufacture dirt on former Vice President Joe Biden and his son ahead of the 2020 election.

"You walk down the halls, and there was this sense of dread, and everyone's kind of thinking, did the president really do this?" one FBI special agent told Insider.

Officials are also frustrated by the Justice Department's decision not to launch a criminal investigation into allegations in a whistleblower complaint accusing Trump of breaking campaign-finance laws.

The Justice Department's handling of the matter added to concerns about whether the FBI was being "neutered as an organization," a US official told Insider.

Complicating matters is the fact that all this occurred against the backdrop of Attorney General William Barr's investigation into the origins of the Russia probe.

"There's a lot of concern among officials that they're going to get thrown into the blender, that they do all the work and then are ridiculed for it, and accused of facilitating a coup or doing the bidding of the deep state," Frank Montoya Jr., a recently retired FBI agent, told Insider.

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Three years ago, the FBI launched an unprecedented investigation focused on one question: Did President Donald Trump's campaign help a foreign power interfere in the 2016 election?

Now, just months after that investigation was formally closed, FBI officials are stunned the president is openly calling for another country to intervene in another presidential election.

One special agent, who spoke with Insider on the condition of anonymity because they are not authorized to speak to the press, said officials were "rattled" not just by the nature of Trump's actions but also by his brazenness.

"You walk down the halls and there was this sense of dread, and everyone's kind of thinking, did the president really do this?" the agent said.

The agent was one of four current and former officials Insider spoke with about the matter. In addition to feeling undermined by the Justice Department's ongoing investigation into the Russia probe's origins, sources also said FBI officials were frustrated with how the Justice Department handled a criminal referral related to a whistleblower's allegations against Trump, saying it added to a sense that the bureau was being "neutered."

At the heart of the controversy are Trump's repeated efforts to pressure Ukrainian President Volodymyr Zelensky to investigate former Vice President Joe Biden and his son. Biden is one of the 2020 Democratic front-runners and Trump's chief political rival.

Read more: Federal prosecutors are investigating whether Rudy Giuliani violated foreign lobbying laws in Ukraine

Trump ordered his administration to hold up a nearly $400 million military-aid package to Ukraine in July. A few days later, on July 25, the president had a phone call with Zelensky, during which Trump told his Ukrainian counterpart the US "does a lot for Ukraine."

Zelensky acknowledged that and said Ukraine wanted to purchase more Javelins — a powerful US-made anti-tank missile — from the US. Trump immediately followed up and told Zelensky he would like Ukraine to "do us a favor, though," and investigate Biden.

Trump made no direct mention of the aid package, but his request was alarming enough to White House officials and others on the call that they began discussing how to "lock down" all records of the conversation, and White House lawyers immediately began working on damage control, according to a whistleblower complaint a US intelligence official filed against Trump in August.

Trump with Ukrainian President Volodymyr Zelensky. AP Photo/Evan Vucci

Officials are concerned about whether the FBI is being 'neutered as an organization'

One US official who works in counterintelligence told Insider that staff at the bureau were not only "blindsided" by the contents of Trump's call with Zelensky but also frustrated with the Justice Department's handling of the matter.

Michael Atkinson, the intelligence-community inspector general, and Joseph Maguire, the acting director of national intelligence, sent the whistleblower's complaint to the Justice Department for a criminal investigation because of concerns that the president may have violated campaign-finance laws by asking the Ukrainian government to manufacture dirt on his political opponent.

Read more: Trump says he doesn't know if Rudy Giuliani is still his lawyer amid reports that Giuliani is under federal investigation

The Justice Department's criminal division reviewed the whistleblower's complaint and determined that there were no grounds for an investigation of Trump's behavior. Officials are said to have decided that the White House summary of Trump's phone call with Zelensky didn't constitute a campaign-finance violation because he didn't ask for a financial contribution or an "item of tangible value."

They did not interview any witnesses or gather more facts outside of reviewing the summary of the call.

The Justice Department's actions were a departure from the norm because typically, in such cases, the FBI investigates if there was criminal wrongdoing and makes a recommendation to the Justice Department on whether or not to press charges.

Here, the US official said, "the DOJ made the decision right off the bat, and that was viewed by many as a slap in the face and usurping the FBI's independence and judgment." It also added to concerns about whether the FBI was being "neutered as an organization," the official said.

Trump and Attorney General William Barr. Chip Somodevilla/Getty Images

'Everyone says they did their jobs, and yet they're being accused of treason'

Complicating matters is the fact that all this occurred against the backdrop of Attorney General William Barr spearheading a separate investigation into the origins of the Russia probe.

There is no evidence that the FBI or the Justice Department acted inappropriately while investigating Russia's interference in the 2016 election. But Trump and his allies in Congress and the media have long called for an investigation into purported corruption and anti-Trump bias within the Justice Department, which they claim was the catalyst for the Russia probe.

Read more: Ex-Ukraine envoy says she was fired on 'unfounded' and 'false' grounds after standing up to Trump and Giuliani

"There's a lot of anger and frustration that this is still going on," Frank Montoya Jr., a former FBI agent who retired in 2016, told Insider, referring to the continued focus on the bureau's handling of the investigation. "There's a lot of concern among officials that they're going to get thrown into the blender, that they do all the work and then are ridiculed for it, and accused of facilitating a coup or doing the bidding of the deep state."

Montoya added that one official told him they believe "this thing's going to be open until Trump is no longer president because they want to find something even if there's nothing there."

"Everyone says they did their jobs, and yet they're being accused of treason, and they can't stand that," he said. "It drives them crazy."

The FBI's J. Edgar Hoover headquarters building in Washington. AP

Trump is 'fanning the flames of his own political demise'

A former senior FBI official echoed that assessment, telling Insider that fear is a big part of why people at the FBI and the Justice Department haven't spoken out the way the whistleblower did.

"This person followed all the established laws and protocol for reporting genuine allegations of misconduct," the former official said. "And still, there's no real guarantee that even the protections of the law are going to keep their life from being turned upside down."

That said, intelligence veterans warn that the president's apparent lack of awareness of the quicksand he's in could be his undoing — it was Trump who ordered the release of the Ukraine phone-call memo that confirmed he'd pressured Zelensky to open an investigation.

Read more: These are the key players you need to know to make sense of the Trump impeachment inquiry

Right now, House Democrats are in the middle of a brewing impeachment inquiry examining Trump's efforts to pressure the Ukrainian government to investigate Biden and his son. The White House has responded by stonewalling Congress at every step by refusing to turn over documents and blocking witnesses from testifying.

But by obstructing the inquiry, legal experts told Insider last week, the president is giving Congress more reasons to impeach him.

Montoya agreed.

"He's fanning the flames of his own political demise," he said. "The rope is tightening around his neck, and he doesn't realize it because he's too busy enjoying the high."