President Donald Trump. Thomson Reuters Deputy Attorney General Rod Rosenstein appointed a special counsel on Wednesday to oversee the FBI's investigation into Russia's election interference and whether the Trump campaign colluded with the Kremlin.

The probe is now under the purview of Robert Mueller, a former FBI director, who has been praised by his former colleagues, national-security experts, and members of Congress on both sides of the aisle.

After learning of the appointment, Trump said in a statement, "I look forward to this matter concluding quickly.

"As I have stated many times, a thorough investigation will confirm what we already know — there was no collusion between my campaign and any foreign entity," he said.

Many of his advisers framed it as a positive development, since the White House could avoid questions about the investigation and refer them to Mueller.

However, a person in the room with Trump and his aides when they heard of Mueller's appointment said "everyone knew this wasn't good news," according to Politico.

Max Boot, a foreign-policy analyst, tweeted a similar assessment on Wednesday. He said the White House was "desperately spinning the special counsel as good news, but a retired FBI agent tells me Mueller will 'crush' Trump."

Scott Olson, a former FBI agent who recently retired after three decades at the bureau, told Business Insider on Wednesday that Mueller was "a good choice for this investigation."

"Not only is he a seasoned prosecutor, he has a good level of experience in national-security investigations and issues," Olson said. "I think we can expect him to focus on developing a solid understanding of the facts — what actually happened — and then follow with a thoughtful recommendation regarding who, if anyone, should be held accountable."

'Make no mistake: This is bad news for President Trump'

Trump fired FBI Director James Comey on May 9 amid the bureau's investigation into Trump's ties to Russia, prompting Democrats and national-security experts to call for a special counsel. Those calls became louder when The New York Times reported this week that Trump had asked Comey to drop the bureau's probe into Michael Flynn, the former national security adviser.

"People across the political spectrum should be able to breathe a sigh of relief at the appointment of Robert Mueller," said Andy Wright, a professor of constitutional and criminal law at Savannah Law School.

"He begins this process with the bipartisan gravitas that can reassure to have confidence in the criminal and counterintelligence investigation," Wright added. "Make no mistake, though: This is bad news for President Trump."

Trump with Attorney General Jeff Sessions. AP Photo/Evan Vucci

Robert Deitz, a former top counsel for the National Security Agency and the CIA who worked with Mueller when he headed the FBI, said he had "enormous respect" for Mueller. He echoed Wright's assessment that Mueller's appointment meant that "the president may have gone from the frying pan into the fire."

Wright said that Mueller, unlike Rosenstein, enjoyed political independence and that Trump would pay a "much higher price" if he were to fire Mueller than he did for firing Comey. Most Republicans openly supported Comey's dismissal but reacted with alarm when they heard that Trump asked Comey in February to drop the Flynn investigation.

"Trump won't have the ability to influence or impede this investigation without severe consequences," Wright said. "The special counsel doesn't have additional power, but he has independence. Unlike Rosenstein, Mueller doesn't have to run the broader Department of Justice. Therefore, he gets to avoid the awkwardness of investigating, say, Attorney General Jeff Sessions' conduct while sitting through five other meetings a day with him."

The FBI reportedly examined Sessions' interactions with Russia's ambassador to the US, Sergey Kislyak, last year — which he failed to disclose during his Senate confirmation hearings — as part of its investigation into Russia's election interference.

"In addition," Wright said, "Mueller will enjoy a base of support in Congress that will be wary of any efforts to clip his wings."

Lawyer up?

Trump's advisers have recommended he hire a private lawyer to deal with the Russia investigations, according to The New York Times. It would not be unprecedented: President Bill Clinton hired a personal counsel, David Kendall, in the early 1990s amid the FBI's Whitewater probe.

Wright said Trump couldn't depend on White House lawyers, like counsel Don McGahn, to defend him because "his use of them in a defense could transform them into instruments of obstruction of justice."

"He needs to hire private criminal counsel," Wright said. "White House lawyers represent the Office of the President and not Donald J. Trump."

In any case, Wright said, McGahn is becoming "a fact witness in his own right" regarding Trump's relationship with Flynn.

Former acting Attorney General Sally Yates told a Senate Judiciary subcommittee earlier this month that she warned McGahn about Flynn's conversations with Kislyak in January so the Trump administration "could take action" amid concerns that Flynn was subject to blackmail by the Russians.

Any private counsel Trump hires would have their work cut out for them, given the president's penchant for out-of-court comments — like his frequent use of Twitter.

Beth Wilkinson, a former Justice Department prosecutor, told Reuters that Trump's comments last year about the judge overseeing his Trump University fraud case — he called the Indiana-born judge a "hater" and noted his Mexican heritage — "shows the difficulty of having a client who won't listen."

When it comes to examining whether Trump sought to obstruct the FBI's investigation into Russia's election interference and whether the Trump campaign played a role, experts say the president's pattern of behavior and past statements about the probe will likely come back to haunt him. (Trump's comments about barring Muslims from the US were similarly considered when federal courts were debating the intent behind his two controversial executive orders on immigration.)

The president "needs a sophisticated lawyer who has dealt with cases at the intersection of criminal law and politics," a Washington lawyer involved in several White House investigations told Reuters on Wednesday. "He is flunking all the rules of crisis management."

The White House did not respond to a request for comment.