Sixteen years ago, Abdi Nor Iftin was a Somali refugee living in one of the roughest slums in Kenya when he found out he had won the lottery of a lifetime. Out of nearly eight million applicants in 2013, he had been one of the lucky 50,000 granted a US visa through a scheme known as the diversity visa scheme that the US government had begun in the 1990s.

Abdi had long dreamt of moving to America. He was so obsessed, his childhood friends even nicknamed him "Abdi America" after he learnt to speak English by watching Hollywood movies. "My whole life I have been in love with America - the best country in the world, the dreamland, the land of opportunity," he told the BBC in 2014.

That year, Abdi, now 41, arrived in the US, settled in a small town in Maine, got a job installing insulation and became a US citizen. But now, his hopes have run up against reality. He lost his job at a refugee resettlement agency this year, and consequently his health insurance.

On the eve of the United States' 250th birthday, Abdi, like many Americans, is feeing uneasy about the future of his country.

Meanwhile, Luke Mullen, a 24-year-old actor from California, told me he's planning on moving to Canada because of a lack of film opportunities in Hollywood, of all places.

"Wealth is getting consolidated in this country and as that happens, the opportunities are dwindling," he said.

Survey after survey taken ahead of the 250th anniversary of America's founding shows many Americans feel the "American Dream"- the promise that anyone in the United States can create a bright future for themselves - is fading.

A recent poll from the Associated Press-NORC found that only a third of the public believes the American Dream still exists. The sentiment is the same across many surveys. One recent study from the Pew Research Center, shows that most Americans say the country's best days are behind it.

America's 250th birthday also comes at a moment of deep polarisation and partisan divide.

So what does it mean if the Dream - a brand exported around the world in movies, music and pop culture - feels out of reach?

'Not a dream of motor cars'

In those early days after the Revolutionary War and well into the 21st Century, what became known as the Dream enticed millions of immigrants to this shiny new nation full of hope, optimism and individualism. Factory workers, farmers, gold diggers, frontiersmen flocked to the US with the belief that they could create a new identity - an "American" - unshackled from the class systems of Europe.

Historians will tell you that the Dream never included everyone - certainly not Native Americans, slaves, or even women. Nevertheless, the idea of the American Dream persisted.

The concept of the American Dream dates back to the founding of the US, but the phrase wasn't popularised until later, in The Epic of America, a book published in 1931 during the Great Depression.

In it, the historian James Truslow Adams wrote: "It is not a dream of motor cars and high wages merely, but a dream of social order in which each man and each woman shall be able to attain to the fullest stature of which they are innately capable."

Over the years, the slogan has evolved. These days it's often associated with entrepreneurialism, social mobility and, above all, economic opportunity.

"It has always been about doing better in life than before," says Cyril Ghosh, author of The Politics of the American Dream: Democratic Inclusion in Contemporary American Political Culture. "For some people, the better in life is simply not being persecuted by the Church of England.

"It's not only about materialism. It's about security. It's about doing better than a previous station. That's what it's always been about."

Abdi had grown up in Somalia, hiding in dugouts to avoid getting shot by the militant group al-Shabab.

"Freedom was a huge priority. Living the next day, breathing next day, was a big, big issue, and I really wanted that," he said, explaining why he had wanted to move to the US.

Researchers say first-generation immigrants, like Abdi, are often more upbeat about the potential of America.

"Many are coming from less wealthy nations. And so they really are going to end up doing better than if they had not emigrated," says Elizabeth Suhay, author of Debating the American Dream: How Explanations for Inequality Polarize Politics.

"Immigrants, for the most part, are more likely to say that they are achieving the Dream, or they've achieved it," said Mark Hugo Lopez, director of race and ethnicity research at the Pew Research Center who has specifically looked in-depth at attitudes among Latino immigrants. They also tend to be, Lopez said, more optimistic about the prospects for their children.

American Dream interrupted

The American Dream has always been a sell for immigrants. However, fewer of them are coming these days.

President Trump has made curbing immigration a cornerstone of his presidency, after campaigning on a promise to carry out the largest mass deportation programme in history.

During his second term, Trump has not only clamped down on the number of immigrants illegally entering via the southern border, he has blocked some legal pathways to come to the US, including the diversity visa programme that Abdi used.

But today it's not just that the US is welcoming fewer immigrants, it also appears a record number of people may be leaving.

One suggestion is that many Americans who grew up in the US don't think the country has held up its end of the bargain - that if you work hard and you play by the rules, you should have a decent, comfortable life.

Last year, in a historic reversal, the number of Americans moving to Ireland was higher than the number of Irish moving into the US. The US government doesn't track the number of Americans voluntarily leaving the country, so there aren't official statistics, but reporting suggests it's not just Ireland.

A record number of Americans are applying for UK citizenship, and The Wall Street Journal reported that the number of Americans arriving to live and work in nearly all of the EU's 27 member states is rising.

Why are people leaving? Some point to current US politics, others to healthcare costs and the overall standard of living. In most cases it is likely to be for a variety of reasons, some of them personal.

For Luke Mullen, it's about job prospects.

The actor, who starred in the Disney show Andi Mack as a teen and has now become more involved with writing and production, says he has more opportunities for film projects these days in Vancouver, Canada than he does in southern California. Vancouver is covered by new government tax credits to try to help it compete with Hollywood and become a major movie hub. (BBC)