The evening before Comey's testimony, Marc Kasowitz was spotted buying a box of cigars, and sources overheard him saying, "We won. Trump's in the clear. ... It's clear Trump didn't do anything wrong."

He continued his celebration the next day, declaring, "The President feels completely vindicated."

But former prosecutors say it's far too early to pop the champagne.

On the other side of Pennsylvania Avenue, special counsel Robert Mueller has been quietly and methodically building the equivalent of a small US attorney's office -- a team of formidable legal minds who've worked on everything from Watergate to Enron, unlikely to leave any stone unturned.

Legal dream team in white shirts and dark suits

Right out of the gate, Mueller brought on three partners from his former law firm, WilmerHale, with significant litigating experience in high stakes cases: Aaron Zebley, who previously served as Mueller's chief of staff at the FBI; Jeannie Rhee, a former federal prosecutor and top official at the Justice Department's Office of Legal Counsel; and James Quarles, who worked on the Watergate investigation as a young prosecutor.

Rhee's past work on behalf of the Clinton Foundation is unlikely to go ignored by Trump supporters -- though others at WilmerHale, such as Jamie Gorelick, currently represent Trump's immediate family members.

Mueller has also reportedly recruited skillful prosecutors from within the highest levels at DOJ -- including Andrew Weissmann, chief of the Criminal Division's fraud section, who served as former director of the Enron Task Force and general counsel under Mueller at the FBI.

Jared Kushner's New York Observer ran a series of scathing stories depicting Weissmann and then Assistant Attorney General Leslie R. Caldwell as strong-arm prosecutors that " ran roughshod " over defendants' rights during the Enron investigation, but during his tenure with DOJ, he's won a series of honors, including the Attorney General's Award for Exceptional Service in 2006.

But perhaps the most significant hire to date was reported by the National Law Journal on Friday: deputy solicitor general Michael Dreeben, a prolific Supreme Court advocate who oversees the Justice Department's criminal appellate docket.

Preet Bharara -- former US attorney of the Southern District of New York, who has had his own tussle with Trump and had a ringside seat to Comey's testimony Thursday -- tweeted that Dreeben is one of the "top legal and appellate minds at DOJ in modern times."

"It appears that Bob Mueller is recruiting the smartest and most seasoned professionals who have a long track record of independence and excellence," added Bharara.

And former acting US solicitor general Neal Katyal, who is a partner at Hogan Lovells and one of the lead attorneys for Hawaii in the travel ban lawsuit against Trump, agrees that the choice of Dreeben is telling.

"You don't bring Michael Dreeben onto something ordinary," said Katyal. "He's the top criminal law practitioner in the United States."

Impeccable legal credentials aren't the only requirement for this work, however.

Mueller has set the tone at the top with a dress code -- even if only for himself -- showing he means business. A source tells CNN he is back to his old uniform from his days at the Justice Department and FBI: plain white shirts and dark suits.

That's a departure from his more recent private sector law firm days, when on occasion he was seen wearing a blue shirt or, shockingly to those who worked with him for years, a shirt with a checked pattern on it. During the 12 years he led the FBI, agents knew never to wear anything but a suit, white shirt and a tie, or risk being sent away.

For the moment, the team is holed up in an office building four blocks from Justice Department headquarters. But a source tells CNN there's no secure room to review highly classified material, otherwise known as a SCIF, so the team will likely have to find new quarters at some point.

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A spokesperson for Mueller declined to comment.

'A surgeon's scalpel'

For the President, building a team of qualified lawyers to go toe-to-toe against Mueller has gotten off to a slower start.

Kasowitz -- an aggressive civil litigator and longtime Trump attorney, has been seeking advice from influential DC lawyers on ways to round out the President's defense team, according to one source, but so far has not recruited one of the more well-known lawyers with investigative experience to work with him.

A source tells CNN that Jay Sekulow and Michael Bowe, another attorney at Kasowitz's firm, have joined the defense team. Bowe has represented Trump in past real estate disputes and attended Thursday's news conference after Comey's testimony, standing with Kasowitz. And Sekulow, chief counsel of the American Center for Law and Justice, has already published an op-ed for Fox News arguing "(w)ith his testimony, Comey's case against President Trump collapsed like a house of cards."

Legal experts caution, however, that enlisting the right people with the right experience in this case is essential.

"The worst thing you can do here is use a butcher's meat-ax instead of a surgeon's scalpel," says former federal prosecutor Robert Bennett, who represented President Bill Clinton during the Paula Jones scandal and now practices at Hogan Lovells.

That advice is perhaps even more critical after Comey's testimony on Thursday suggesting that Mueller's investigation may eventually escalate to whether the President obstructed justice by firing Comey.

If Kasowitz's victory speech hinges on Comey's admission this week that he previously said Trump wasn't personally under an FBI counterintelligence investigation that doesn't close the case.

"Bob Mueller's investigation is just beginning," says Kevin Andrew Chambers, white collar partner at Latham & Watkins and former Assistant US Attorney in DC. "It is far too early for anyone to speculate where he will end up and folks should get comfortable with the fact that it could be a couple years before he reports his findings. Remember, he is a career prosecutor. His focus will be on accumulating and reviewing the entire body of evidence rather than fixating on any one document, witness, or event."