The president and first lady were seen at Fiola Mare, a seafood restaurant popular with the political set in the Georgetown area of the city.
"Per CDC guidance and DC Mayor Muriel Bowser's executive order, all individuals over age 2 are required to wear a mask indoors, regardless of vaccination status," the restaurant announces on its website.
"Masks must be always worn while in our restaurants, except while eating and drinking."
Though, the 78-year-old and his wife were both maskless as they walked through the restaurant, with their Secret Service detail wearing black face masks.
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The president was carrying his face mask yet not wearing it, notwithstanding vocally pushing for people to wear them as often as possible.
Despite being fully vaccinated, President Biden has further frequently donned his own mask in what some critics have branded political theater.
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He has announced he is determined to differentiate himself from Donald Trump, known for turning his nose up at the coverings and not being snapped wearing one until July 2020 - five months after cases started to hit US shores.
In August, the Mayor of DC Muriel Bowser reinstated a mask mandate and ordered restaurants, bars, and other liquor-serving establishments to face fines for not enforcing the rules.
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The first violation will be issued with a warning from the Alcoholic Beverage Regulation Administration (ABRA), and the second will point to a $1,000 fine.
After three or more breaches, the DC liquor board will examine the business's liquor license.
Unlike in New York, restaurants are not obliged to insist on evidence of vaccination or a negative test.
The White House has not commented on the Bidens' rule-breaking.
Biden had the "lobster," a patron told the pool reporter - although the only lobster on the menu seems to be a $46 crudo.
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Wild New Zealand langoustine, are likewise available, at $28 each.
Fiola Mare, owned by James Beard Award-winning Chef Fabio Trabocchi, is a frequent haunt of politicians and power launchers: Jared Kushner and Ivanka Trump ate there with Ted Cruz and his wife, while the Obamas were regulars.
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Barack Obama celebrated his birthday there in 2016.
"The Obamas would stroll in like a gorgeous, happy ex, to celebrate a birthday or throw a party for Meryl Streep and Steven Spielberg, and you could feel the whole restaurant swoon," wrote Moe Tkacik, a former server, in a February article for Slate.
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She used the article to denounce members of the Trump administration for being poor tippers and demanding guests.
While the Obamas were regularly seen at DC dining hotspots, Donald and Melania Trump only dined at one restaurant in his own Trump International Hotel.
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