It is two centuries old, spans 30ft by 34ft and has suffered the effects of age and being snipped for souvenir hunters. The original star-spangled banner, the flag that inspired Francis Scott Key to write the song that would become the US national anthem, lies horizontally at a 10-degree angle of elevation in a low light chamber at the Smithsonian National Museum of American History in Washington. Visitors file past silently and reverently as if beholding a religious relic.

“Patriotism: love of country,” Marcia Walker, 71, a retired nurse from Granite City, Illinois, said during a visit on Monday when asked about the meaning of the flag. “It’s not just for the military but it’s a feeling each and every American should have for our justice system and our ability to love and respect each other.”

Such questions have taken centre stage over the past weekend after Donald Trump argued that football players who kneel during the national anthem should be fired. “Courageous Patriots have fought and died for our great American Flag – we MUST honor and respect it!” he tweeted, conflating the stars and stripes with the military.

But just as “USA! USA! USA!” is sometimes chanted on the streets by both Trump supporters and anti-Trump protesters at the same time, the flag and anthem are as contested as the debate over what it is to be American.

After viewing the original flag, made in 1813 by Mary Pickersgill with the help of her daughter, two nieces and an African American indentured servant, museum patrons hear clips from different versions of The Star-Spangled Banner, ranging from traditional to Jimi Hendrix on a Fender Stratocaster at the Woodstock festival in 1969.

His howling, feedback-heavy rendition was widely interpreted at the time as a political statement against the Vietnam war although, according to biographer Charles Cross, when Hendrix was asked to explain its meaning, he replied: “We’re all Americans... It was like ‘Go America!’... We play it the way the air is in America today.”

Jimi Hendrix performing The Star-Spangled Banner at the Woodstock festival in 1969.

Patrons are also shown a video loop of the US flag’s many manifestations: carried by women demanding suffrage, first world war recruits, the Ku Klux Klan marching in Washington, people celebrating victory in the second world war, civil rights marchers in Selma, protesters against the Vietnam war, a prisoner of war returning from Vietnam and participants at a disability rights rally, immigrant rights rally and gay pride march; worn by a freed slave at the end of the civil war; flying in a playground on Ellis Island, New York; hoisted by soldiers in Iwo Jima and firefighters in the ruins of the World Trade Center; hanging at Robert F Kennedy’s funeral train and an Olympic stadium; planted by the first men on the moon.

The flag is also frequently seen flying outside suburban homes – far more so than in other western countries such as the UK. Its appeal is never more evident than at naturalisation ceremonies for new citizens, who often clutch miniature stars and stripes with pride.

The anthem started in an act of military defiance by a young nation seeking to assert its identity. In 1812, the US declared war on Britain, smarting over what it saw as British interference in trade. But it suffered numerous setbacks, including being helpless in August 1814 to prevent British troops marching on Washington and setting the White House ablaze.

A month later, the British spent 24 hours bombarding Fort McHenry, which protected Baltimore. By the “dawn’s early light” on 14 September, the lawyer Francis Scott Key, who was aboard a ship several miles away, could just make out the American flag flying above Fort McHenry. He realised that British ships were pulling out of Baltimore and the US had survived. He began to compose a poem on the back of a letter under the title The Defence of Fort McHenry.

Copies were given to every man at the fort and around Baltimore. The published work included instructions that it be sung to the 18th-century British melody To Anacreon in Heaven. The first documented public performance of the words and music together took place in Baltimore on 19 October 1814. A music shop published the words and music under the title The Star-Spangled Banner.

Heather Cox Richardson, a history professor at Boston College, said: “For Francis Scott Key, it was: ‘Is this republic going to be here tomorrow – a republic entrenched in the Enlightenment idea of democracy – or is America going to be annexed by the British again to become part of an oligarchy?’

“That’s the story of America. It’s a nation built on an ideal, built on ideology, but the ideology is built out of individualism, which is paradoxical.”

It gained special significance during the civil war and, by the 1890s, had been adopted by the military for ceremonial purposes. After a campaign lasting decades, it finally became the official national anthem in 1931.

But in the 1960s, as the Vietnam war raged amid social upheaval, some burned the flag and others rallied in its defence. Ken Burns and Lynn Novick’s epic PBS documentary The Vietnam War explores how the war raised questions of different types of patriotism: among those who fought the war and those who demonstrated against it. In 1968, Congress passed the Federal Flag Desecration Law, making it a federal crime to “knowingly cast contempt upon any flag of the United States by publicly mutilating, defacing, defiling, burning, or trampling upon it”.

Richardson said: “The whole identification of the flag with the right wing really takes off with Richard Nixon. George W Bush takes this to new heights after 9/11. Donald Trump is a loose cannon.”

Marliss Bates, a 73-year-old African American teacher from Louisiana, was so engrossed in the information panels on Monday that she walked past the giant flag without noticing. Before heading back for a second look, she said: “It’s freedom, liberty. That’s what it’s supposed to mean. Francis Scott Key could see the flag waving so that meant we were still free people.”