In video footage, President Donald Trump can be seen with his hand over his heart as the Star-Spangled Banner starts to play but he doesn't sing all of the words of the anthem. "And we want our national anthem respected also".
According to the code, during a rendition of the anthem, everyone present must stand at attention facing the flag with their right hand over their heart.
Before heading to the college national football championship on Monday, President Trump reiterated his views on athletes using the national anthem to protest racial discrimination and police violence in America.
While the president did not respond to criticism of his lack of singing, he did update his Twitter photo to a picture of himself during Monday night's national anthem.
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Alabama running back Bo Scarbrough was caught on a camera yelling "F*** Trump" in a tunnel ahead of the game.
"As a military veteran who has watched Trump, a coward who never served and received five draft deferments, slam Colin Kaepernick as unpatriotic for peacefully protesting, I am beyond livid that he doesn't know the words to the National Anthem", tweeted Charlotte Clymer, a former aide to Hillary Clinton.
Trump is believed to have left the game after the first half, thereby missing the half-time entertainment from rapper Kendrick Lamar, who is no fan of the president. He has publicly blasted several players past year for not respecting the anthem or the flag.
Added another, "Trump was mouthing some words during parts of the national anthem, but it was unclear what he was saying".
Later, Trump took to Twitter praising Pence for leaving the game. In October 2017, he had also asked Vice President Mike Pence to leave an Indianapolis Colts game early after the players knelt during the National Anthem. Trump later tweeted that he told Pence to leave the stadium "if any players kneeled, disrespecting our country".