Current and former FBI and DOJ officials expressed shock and frustration at President Donald Trump's appointment of Matthew Whitaker as acting attorney general.

"Seriously? This guy?" one current FBI agent told INSIDER. "No words."

A former DOJ official expressed a similar sentiment, saying department employees have been "in a daze" since Whitaker's appointment "and have been for a while," and that local assistant US attorneys are also "pretty embarrassed."

Whitaker is seen as a staunch Trump loyalist and has publicly mused about gutting the Russia investigation. He is now overseeing the special counsel Robert Mueller.

DOJ veterans and constitutional law experts argue that Mueller could challenge Whitaker's appointment on constitutional grounds if he overruled a decision by the special counsel.

President Donald Trump's decision to oust Attorney General Jeff Sessions this week and replace him with acting Attorney General Matthew Whitaker sent shockwaves through Washington.

It also turned heads at the FBI and the Department of Justice (DOJ), which Whitaker will oversee until Trump nominates and the Senate confirms a permanent replacement.

One current FBI agent was blunt when asked about Whitaker's appointment.

"Seriously? This guy?" the agent, who requested anonymity to speak candidly, told INSIDER. "No words."

Frank Montoya Jr., a recently retired FBI special agent, said the predominant mood within the bureau is "angst."

"There is a lot of angst about what [Whitaker's] appointment means largely because, contrary to what Trump or his supporters say, folks in the DOJ and the FBI actually pride themselves on their objectivity," Montoya told INSIDER. "I spent a lot of time in meetings at all levels of the bureaucracy, and partisan politics never drove the decision making process. There is a lot of angst that someone like Whitaker may try to change that."

Read more: Robert Mueller has reportedly begun drafting his final report in the Russia probe

While he was Sessions' chief of staff, Whitaker reportedly met with Trump in the Oval Office over a dozen times. And according to The Washington Post, whenever Trump complained about the ongoing Russia investigation Whitaker "often smiled knowingly and nodded in assent."

The Russia investigation, spearheaded by the special counsel Robert Mueller, has been a thorn in Trump's side since shortly after he took office. In addition to investigating Russia's interference in the 2016 election, Mueller is also looking into whether members of the Trump campaign colluded with Moscow to tilt the race in his favor, as well as whether Trump sought to obstruct justice after learning of the investigation's existence last March.

The special counsel is said to be nearing the end stages of the Russia probe — he has reportedly begun writing his final report — and Whitaker's appointment raises new questions about the fate of the investigation.

"This decision is unsurprising," another current FBI agent told INSIDER. "POTUS has always wanted to replace Jeff Sessions with someone loyal to him. He values personal loyalty above all else, including rule of law. Another sad day for the country."

President Donald Trump on Thursday delivered remarks on immigration and border security at the White House. Kevin Lamarque/Reuters

People at the DOJ are 'in a daze' and 'pretty embarrassed'

Once described as the West Wing's "eyes and ears" in the DOJ, Whitaker made the rounds on right-wing media over the last two years claiming without evidence, that there was "no collusion" between the Trump campaign and Russia.

He also said in a CNN op-ed last year that Mueller had overstepped his mandate by digging into the Trump Organization's finances.

And late Thursday, audio footage resurfaced of Whitaker claiming the "left is trying to sow this theory that essentially Russians interfered with the US election, which has been proven false. They did not have any impact in the election."

The US intelligence community concluded last year that Russia mounted an elaborate campaign to meddle in the 2016 election to elevate Trump to the presidency. The assessment did not reach a conclusion about whether Russia's meddling had an impact on the results.

In another recording reported on by Mother Jones, Whitaker said the president cannot obstruct justice and can kill any investigation he wants.

"Main Justice people are in a daze" since Whitaker's appointment "and have been for a while," one former DOJ official — who requested anonymity to freely discuss the mood within the department — told INSIDER. "Local [assistant US attorneys] are keeping their heads down and just doing their work but are pretty embarrassed, particularly in New York and Chicago."

Montoya described a similar atmosphere.

"The Whitaker appointment was a slap in the face to every lawyer at DOJ," he said. "It was also an insult to everyone at FBI, and particularly, those working with the special counsel. Not only did he prejudge ... he did so without any direct knowledge of the case. His other peccadillos — about the scam artist he once worked for and his comments on non-Christian judges — only add to the offense."

The Post reported that despite Whitaker's controversial remarks about Mueller and the Russia probe, the acting attorney general has no plans to recuse himself, even if DOJ ethics officials urge him to do so. Sources also told The Post that Whitaker would likely oppose a request from Mueller to subpoena the president if it came down to it.

A former senior DOJ official, who worked closely with Mueller when he was the FBI director, told INSIDER that although the special counsel is "as by-the-books as it gets, he likely won't take it lying down if he thinks the integrity of his investigation has been compromised."

Robert Mueller. AP

Is Whitaker's appointment constitutional?

The myriad questions surrounding Whitaker's independence prompted DOJ veterans and constitutional-law experts to begin laying the groundwork to argue that Mueller could challenge Whitaker's appointment if he overruled a decision by the special counsel.

Attorneys Neal Katyal and George Conway wrote in a New York Times op-ed that because a "principal officer" of the US must be confirmed by the Senate, "President Trump's installation of Matthew Whitaker as acting attorney general of the United States after forcing the resignation of [former Attorney General] Jeff Sessions is unconstitutional. It's illegal. And it means that anything Mr. Whitaker does, or tries to do, in that position is invalid."

The argument has also gained steam in some conservative-leaning circles.

"Just to be clear, you can have an acting Attorney General," tweeted conservative commentator and Trump critic Erick Erickson. "See e.g. Sally Yates. But you cannot have an acting AG who had not been through a confirmation process for an AG position. Yates was confirmed as a Deputy AG. Whitaker has not."

But there isn't unanimous consensus among experts on the issue.

Steve Vladeck, a law professor at the University of Texas, wrote in a Times op-ed that Trump's designation of Whitaker as acting attorney general is constitutional, as long as it is temporary.

Ultimately, legal scholars say, the issue may end up being decided by the Supreme Court.