Treasury Secretary nominee Steven Mnuchin started celebrating his new job early at the Trump Hotel lobby bar in Washington, D.C. on Monday, when he got the hotel staff to saber open his bottle of champagne.

The Trump cabinet pick, who still faces a Senate confirmation grilling on Thursday and reportedly has transition staffers concerned about his readiness, was clearly in good spirits in the Trump Hotel lobby bar, where he was spotted sharing a table with a crowd of friends.

The casually-dressed group appeared to include Mnuchin's fiancée – 36-year-old Scottish actress Louise Linton – as well as a man wearing a Trump hat and several women.

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Couple: Steve Mnuchin, who will run the nation's finances as treasury secretary, was with actress Louise Linton, his fiancée, when he indulged in champagne at the Trump hotel

Here it goes: Donald Trump Jr previously published pictures of champagne bottles being sabred open at Trump International in Washington D.C.

At one point, the group ordered a bottle of champagne – which can run anywhere from $112 for Moet Imperial to $895 for 2004 Dom Perignon rose on the public menu – and it was brought over on a cart.

After ringing a large bell, the hotel's food and beverage director ceremoniously sabered the top of the bottle off with a long knife, a nightly occurrence at the Trump Hotel.

Axios reported on Tuesday that some transition staffers are concerned about Mnuchin's preparedness for Thursday's confirmation hearing, saying he came off as 'uneven and stiff' during practice sessions and additional advisors had to be brought in.

They also expect his hearings might be interrupted by anti-capitalist demonstrators.

Like Trump, the 54-year-old former Goldman Sachs partner is twice divorced. He has three children.

His fiancée, Linton, is a Scottish actress and film producer who has appeared on the TV show CSI.

After graduating from Yale, Mnuchin spent nearly two decades at Goldman Sachs.

He left in 2002 and founded a hedge fund called Dune Capital Management. He is also an avid investor in films, including Avatar and American Sniper.

Similar to other Trump cabinet picks, Mnuchin is personally very wealthy. Fortune estimated this week that his net worth is as high as $400 million - ten times what others had previously suggested.

Preparation: The Trump International Hotel was surrounded by the National Guard on Sunday during a rehearsal of the inauguration

Ready inside and out: The Trump hotel is festooned with red white and blue inside the lobby and has staging outside in readiness for the inauguration celebrations

Also at the hotel: Katrina Pierson, a former Trump campaign spokesman, and senior advisor Boris Epshteyn

SHOWY WAY TO OPEN CHAMPAGNE The practice of using a sabre to open champagne is said to date back to the Napoleonic War. The sabre, a relatively short, curved sword, was the standard issue weapon for French cavalry. It is claimed that dashing young officers perfected the method of forcing open a bottle using the blunt side of the sword moved rapidly and forcefully against the neck. Using the sabre to successfully open a bottle depends on hitting the seam in the glass at the top of the bottle's neck. The very top of the bottle is then forced off by the pressure of the champagne and can fly as far as 30 feet. Done incorrectly, glass shards can turn up in the champagne. But an expert can do it with virtually no risk of glass granules in the drink. Advertisement

Mnuchin wasn't the only one getting ready to celebrate on Monday.

Trump Hotel, which is just down the road from the White House on Pennsylvania Avenue, is also getting decked out for the inauguration on Friday.

Bags of red, white and blue balloons were strung along the 200-foot tall glass ceiling in the atrium lobby, in preparation for a balloon drop after the ceremony.

The Trump Hotel has been the subject of some controversy in Washington.

Critics have grumbled that the Trump Hotel presents a conflict of interest for the president-elect because foreign officials and lobbyists might stay there to try to curry favor with the administration.

As part of a voluntary ethics agreement, Trump's attorneys have said he will 'donate all profits from foreign-government payments made to his hotels to the U.S. Treasury.'

The hotel opened last September after extensive renovations. It is located in the Old Post Office Pavilion, an historic building which Trump leased from the federal government in 2013.

Other Trump insiders spotted at the hotel on Monday evening were communications advisor Boris Epshteyn – who amiably downed a shot of Jameson with a visiting Marine officer – and former campaign spokesperson Katrina Piersen.