For a time, it felt like the attack that shattered America had also brought it together.
After Sept. 11, signs of newfound unity seemed to well up everywhere, from the homes where American flags appeared virtually overnight to the Capitol steps where lawmakers pushed aside party lines to sing "God Bless America" together.
That cohesion feels vanishingly distant as the 15th anniversary of the attacks arrives Sunday. Gallup's 15-year-old poll of Americans' national pride hit its lowest-ever point this year. In a country that now seems carved up by door-slamming disputes over race, immigration, national security, policing and politics, people impelled by the spirit of common purpose after Sept. 11 rue how much it has slipped away.
Jon Hile figured he could help the ground zero cleanup because he worked in industrial air pollution control. So he traveled from Louisville, Kentucky, to volunteer, and it is not exaggerating to say the experience changed his life. He came home and became a firefighter.
Hile, who now runs a risk management firm, remembers it as a time of communal kindness, when "everybody understood how quickly things could change ... and how quickly you could feel vulnerable."
A decade and a half later, he sees a nation where economic stress has pushed many people to look out for themselves. Where people stick to their comfort zones.
"I wish that we truly remembered," he says, "like we said we'd never forget."
Terrorism barely registered among Americans' top worries in early September 2001, but amid economic concerns, a Gallup poll around then found only 43 percent of Americans were satisfied with how things were going.
Then, in under two hours on Sept. 11, the nation lost nearly 3,000 people, two of its tallest buildings and its sense of impregnability. But out of the shock, fear and sorrow rose a feeling of regaining some things, too - a shared identity, a heartfelt commitment to the nation indivisible.
Stores ran out of flags. Americans from coast to coast cupped candle flames and prayed at vigils, gave blood and billions of dollars, cheered firefighters and police. Military recruits cited the attacks as they signed up.
Congress scrubbed partisanship to pass a $40 billion anti-terrorism and victim aid measure three days after the attacks, and approval ratings for lawmakers and the president sped to historic highs. A special postage stamp declared "United We Stand," and Americans agreed: A Newsweek poll found 79 percent felt 9/11 would make the country stronger and more unified.
"I really saw people stand up for America. ... And I was very proud of that," recalls Maria Medrano-Nehls, a retired state library agency worker in Lincoln, Nebraska. Her foster daughter and niece, Army National Guard Master Sgt. Linda Tarango-Griess, was killed by a roadside bomb in Iraq in 2004.
Now, Medrano-Nehls thinks weariness from the wars in Iraq and Afghanistan and combative politics have pried Americans apart, and it pains her to think of the military serving a country so torn.
Larry Brook can still picture the crowd at a post-9/11 interfaith vigil at an amphitheater in Pelham, Alabama. The numbers seemed a tangible measure of an urge to come together.
Now? "I don't think we're anywhere close," says Brook, who publishes Southern Jewish Life magazine. To him, political partisanship and clashes over Middle East policy are walling off middle ground.
Three days after 9/11, Joseph Esposito was at smoldering ground zero as Republican President George W. Bush grabbed a bullhorn and vowed the attackers "will hear all of us soon." The moment became an emblem of American strength and resolve, and Esposito, then the New York Police Department's top uniformed officer, was struck by "the camaraderie, the unity" of those days.
He remembers the support police enjoyed then, and how much the tone had changed by the time of the Occupy Wall Street protests in 2011, when police arrested hundreds of demonstrators, many of whom said cops unjustly rounded and roughed them up. Now the city's emergency management commissioner, Esposito has watched from the sidelines as a national protest movement has erupted in recent years from police killings of unarmed black men, and as police themselves have been killed by gunmen claiming vengeance.
These days, Esposito hopes his job can be unifying. He wants people to feel that the city helps neighborhoods equally to handle disaster. "The 1 percenters should not be better prepared than the 99 percent," he says.
"If everyone feels they're getting their fair share," he adds, "it fosters better feelings toward one another."
For all the signs of kinship after Sept. 11, the first retribution attack came just four days later, authorities said.
Balbir Singh Sodhi was shot dead while placing flowers on a memorial at his Mesa, Arizona, gas station. Prosecutors said the gunman mistook Sodhi, an Indian Sikh immigrant, for an Arab Muslim.
Seeing hundreds of people gather in solidarity on the night of his brother's death showed me "the greatness of unity," says Rana Singh Sodhi, of Gilbert, Arizona. But in the last two years, he's felt a "change toward hatred again." He worries politicians are stirring animosity toward immigrants and minorities.
So does Imam Abdur-Rahim Ali.
After 9/11, he invited first responders for tea and coffee at the Northeast Denver Islamic Center to show appreciation and emphasize that Muslims "are regular Americans." Now, Ali, who is African-American, believes Muslims and people of color are being demonized with "incendiary and divisive" remarks.
"We can't act like racism hasn't been a part of all this," he says.
Can the United States feel united again?
Some Americans fear it will take another catastrophe, if even that can shift the climate. Others are looking to political leaders to set a more collaborative tone, or to Americans themselves to make an effort to understand and respect one another.
When Sonia Shah thinks about the push and pull of American unity since the attacks that killed her father, Jayesh, at the World Trade Center, she pictures a rock hitting a pond.
The innermost ripple, that's the tight circle of support that came together around the people most directly affected by tragedy. Outside it, bigger and more diffuse, are bands of debate over policies and politics in the wake of 9/11.
"We usually see the outer rings of the arguments," says the Baylor University senior. "But I think there always is a current of unity that goes underneath things."