(CNN) With Adele's song "All I Ask" playing in the background, a Maryland teenager opened her computer and wrote an emotional letter to President Barack Obama.

"I am an American, I grew up here. I say the Pledge of Allegiance every day," Aleena Khan told the President. "And yet, I am a Muslim."

Which one, she asked, is she allowed to be?

This series explores the lives of Muslims in the age of ISIS and Islamophobia.

Aleena is 17, with a bright smile and dark hair that sweeps across her shoulders. Her mother is Indian-American, her father emigrated from Pakistan. Aleena and her two sisters have lived in Maryland their whole lives.

Last year, as part of an honors research project on identity crises among Muslim-American teenagers, Aleena spent hours online combing through public comments on news articles about Muslims. What she read shocked her.

"Kick them all out and put the rest in detainment camps. Enough with the PC feces," said one commenter.

"The only peaceful and moderate Muslims are the dead ones," said another.

The tweet from the man wearing military camouflage was the worst, Aleena said. "Hard to tell what we should build first. A border wall or a gas chamber for Muslims."

Aleena sat on the floor of her room, stunned. These people were talking about her mother, her father, her sisters, her cousins, her friends. They were talking about her. If it were just one comment, she could ignore it. But there were so many.

"This is what people think about me?" she wondered. "If I go out and say I'm Muslim will my friends still be my friends? Will people like me anymore?"

She texted her best friend, Haley, telling her what people were saying about Muslims. People are ignorant, Haley answered.

It's difficult to measure a sentiment such as Islamophobia, the word for hatred and fear of Muslims. But it's also hard to escape the idea that living in America today is like watching comment sections spring to lurid life. The anti-Muslim rallies, the vicious hate crimes, the racial profiling, the threats and taunts and questions about divided loyalties.

"Do we really have a choice?" Trump said . "We're trying to be so politically correct in our country, and this is only going to get worse."

Even before the recent attacks, American Muslims say they live under a dark cloud of suspicion. In 2014, they surpassed atheists as the country's "least accepted" religious group.

An estimated 3.3 million Muslims live in the United States, and between September 11, 2001 and the end of last year, 344 have been involved in violent extremism, according to the Triangle Center on Terrorism and Homeland Security . That number does not include attacks from this year, such as the shooting at an Orlando nightclub by Omar Mateen , who killed 49 people

Still, violent extremists are outnumbered nearly 10,000 to 1 in the United States, which means that Omar Mateen is not the norm. Aleena Khan is.

Aleena graduated from Northwest High School in Germantown, where she gave tours to guests, was a member of four honor societies and ran the Green Club with her friend Haley, helping the school earn Green Ribbon environmental status -- "a nationally recognized thing," she says with a smidge of satisfaction. One of the few clubs she didn't join is the Muslim Student Association, though she regularly reads the Quran and attends religious classes and Friday prayers at a local mosque. "I didn't want to separate myself from the rest of my classmates," she said.

In her free time, Aleena has tutored young children, interned at a Christian clothing website and volunteered for a company that helps poor and abused women sell handmade wares. This fall, she began her freshman year at George Washington University in Washington, where she plans to study public policy. She hopes, one day, to improve the foster care system, a goal inspired by a recent documentary.

But being a Muslim in America hasn't been easy, Aleena says, even before the recent rash of Islamophobia.

There's the annual Ramadan challenge, which means skipping lunch with classmates and fasting from water during the dog days of summer. She's doesn't wear shorts, tank tops or bikinis, though many of her friends do. Dating is discouraged, and her parents forbade her from attending the school prom. Friends tried to cheer her up, insisting the dance wasn't that fun, but Aleena saw the pictures, and it sure looked fun.

If Aleena were an Orthodox Jew or conservative Christian, she might yield to similar restrictions and feel like she was swimming against a cultural riptide. But few would question her American identity or allegiance.

Aleena wrote her letter to Obama on February 3, the day of his first visit to an American mosque as President , a date many Muslims believe was too long in coming. She thanked Obama for his faith in Muslim-Americans. It was like an oxygen tank, she told the President, allowing her to breathe a big sigh of relief.

But even with Obama's encouragement, Aleena held some doubts. Will other Americans really accept her, especially when the country seems so anxious and angry?

"Muslims live in fear that they will be attacked," she wrote in her honors project. "Americans live in fear that Muslims will attack them."

After submitting her letter through the White House website, Aleena felt silly, believing no one would read it. She deleted it from her computer and forgot about it.

Aleena Khan presents her research on Muslim American teenagers at a Maryland school fair.

'So what? They're Muslim'

Most Americans don't actually know any Muslims -- at least, not personally.

More than 6 in 10 have seldom or never had a conversation with a Muslim, according to a study conducted by the Public Religion Research Institute. Most Americans also say they know little (57%) or nothing at all (26%) about Islam.

Those numbers have barely budged in 30 years , even after 9/11, two American-led wars in Muslim-majority countries, local and national outreach campaigns by Muslim mosques and organizations, dozens of terrorist attacks worldwide, high-profile congressional hearings and copious media coverage of Islam. All of which suggests that Americans are not just widely ignorant about Islam and Muslims, they are also oddly incurious.

Few things are more frightening than ignorance in action, to paraphrase a German poet

Heavily armed men have protested outside mosques in Texas and Arizona , arguing that it's their patriotic duty to protect the country from Islam.

Mourners in Raleigh, North Carolina, grieve the shooting deaths of three Muslim students in Chapel Hill in 2015.

American Muslims have been told that a mosque, unlike churches and synagogues, cannot serve as an election polling station . Dozens of communities have fought to keep Muslims from building mosques in their neighborhoods , sometimes threatening violence.

From 2001 to 2015, there were 2,545 anti-Islamic incidents targeting 3,052 Muslims, according to the FBI . Last year, Anti-Muslim hate times surged 67%, reaching a level of violence not seen since the aftermath of the 9/11 attacks, and many Muslims believe hate crimes are underreported by victims and not pursued vigorously by police and prosecutors. This year, the FBI has begun counting anti-Arab incidents as well.

Challenged about Trump's proposed ban on Muslims entering the United States, his spokeswoman, Katrina Pierson, said, "So what? They're Muslim."

A coterie of well-funded pundits and self-proclaimed experts encourage Americans to fear all Muslims and the "creeping" influence of Islamic law in the United States. They cast Muslims as "enemies among us," Trojan horses for an insurgency that will topple the republic and conquer its citizens.

Even many liberal politicians, while insisting most Muslims are peaceful, only mention Islam when speaking about national security and countering violent extremism.

"Islam is not thought of as American religion," said Zareena Grewal, a professor of religious studies at Yale University, "however much Muslim-Americans wish that to be true."

In 2011, more than half of American Muslims under 30 said they had been treated with suspicion, called offensive names, singled out by law enforcement or been physically threatened in the preceding year alone, according to a Pew Center report.

Asad Tarsin, a writer and doctor, lives in California with his wife and three young children.

"I know that they will be integrated in America and fully accept their American identity. My question is whether America will fully accept them."

'The Mohammedan world'

Islamophobia didn't start on September 11. It's intricately entwined with America's oldest idea: that this land is, and should always be, a white Christian nation.

Well before the Pilgrims landed in "New Jerusalem," Columbus had set sail on a mission to find riches to retake "old" Jerusalem from the Ottoman Empire. Centuries later, when Colonists sought to unite the states, anti-federalists railed against the Constitution. Nothing in the new document, they fumed, would prevent a Muslim (or a Catholic) from becoming president.

The first Muslims to arrive en masse came in chains. Scholars estimate that some 10,000 to 20,000 slaves from West Africa were Muslims. A few were granted preferential treatment because they could read and write Arabic, and looked "whiter" than other slaves. They were paraded across the country like prized pets, until they started advocating for their emancipation.

"Such is the bloodthirsty, tyrannical Mahometan negro, who is now travelling himself and suite, up and down through the free states in pomp, with the President's passport in his pocket," snarled one Southern newspaper about a Muslim slave freed by President John Adams.

Within a few generations, African Islam was extinguished, snuffed out by plantation owners who converted their slaves to Christianity.

In the 1880s, Muslim immigrants from the tottering Ottoman Empire began to arrive. Before they were allowed into the country, they were required to sign oaths swearing that they owed no loyalty to the empire's Sultan. Even then, most were not allowed to become citizens.

The United States was committed to the idea that its future depended on its identity as a white Christian nation, said Kambiz GhaneaBassiri, author of "A History of Islam in America."

"The presumption has been that all Muslims are considered suspect until proven otherwise."

The Naturalization Act of 1790 allowed only "free white persons" to become US citizens. After the Civil War, "persons of African descent" were added to the list. By the classifications of the era, most Muslim immigrants were neither. Laws passed in 1917 and 1924 made it even harder for Asian and Middle Eastern Muslims to immigrate and become citizens.

In 1942, a Michigan judge denied a Yemeni man's case for citizenship. Apart from the man's dark skin, he ruled, it was "well-known" that Arabs "are part of the Mohammedan world ... and a wide gulf separates their culture from the predominantly Christian peoples of Europe."

Those Christian peoples, of course, trace their religious roots to the Middle East -- the very region the judge deemed irremediably "Mohammedan." By that logic, Muslim immigrants argued, Jesus himself could not be an American citizen. The judge was not persuaded.

Even Muslims born and raised in the United States were considered suspicious, especially if they were not white. As thousands of blacks embraced new, Islam-inspired movements such as the Moorish Science Temple and Nation of Islam in the mid-20th century, the FBI kept a nervous watch.

"Though it did not produce peer-reviewed scholarship," writes scholar Edward Curtis, "the FBI was by far the most prolific student of Muslim groups in the first half of the 20th century."

The FBI's report on the Nation of Islam fretted that black Muslims demonstrate "fearless and outspoken anti-white, anti-Christian attitudes. ... As long as racial inequity continues, the militant and arrogant manner of cult members remains a potential threat of violent action."

In 1965, the United States eased immigration restrictions, opening the door to nearly 3 million immigrants, many economic refugees from countries with sizable Muslim populations.

Pew says that number will climb past 8 million by 2050, when Muslims will become the second-largest religious group in the United States, a surge driven by immigration, large families and the relative youth of American Muslims (their median age in 2010 was 23). Even in 2050, though, Muslims will only make up 2% of the US population.

Islam is the only American religion without a majority race or ethnic group. Muslims living in the United States come from 77 different countries, according to Pew. About 30% describe themselves as white, 23% as black and 21% as Asian. Likewise, every strand of religious commitment is represented here, from puritanical Salafis to mystic-minded Sufis to Muslims who rarely pray or visit mosques.

While many Muslims praise the diversity of their American community, in practice it has made it difficult for them to forge a group identity or rally around common causes and national leaders. More than half of men and 42% of women said no national Muslim group in the United States represents their interests, according to a 2011 Gallup poll

Instead, Muslims have often retreated into ethnic enclaves, hired imams from their homeland and disengaged from the broader culture. Three-fourths of American mosques are dominated by one ethnic group, whether it be Arab, South Asian or African-American, according to a study conducted in 2011 . In the last five years, many American Muslims have worked to make their mosques more diverse.

Still, even Muslims born in the United States have idealized Islamic institutions and leaders overseas, particularly in the Middle East, viewing them as more authentically Muslim. In a strange way, it's as if they agreed with those who argue that Islam is a faith foreign to America.

Even top Muslim scholars and spokesmen have felt the lure of that idea.

Sheikh Hamza Yusuf is co-founder of Zaytuna College in California, the country's first accredited Muslim college. Yusuf, who is white, converted to Islam in 1977 and soon thereafter left the United States to study with Islamic scholars in the Middle East and Africa. When he returned after a decade overseas, he felt lost, spiritually and emotionally.

"I had no context for being an American Muslim," he said. "It was almost like abandoning my American-ness."

Living in 'the grayzone'

Before he went on his murderous rampage at the Pulse nightclub , Omar Mateen googled Sheikh Hamza Yusuf. He might have been seeking Yusuf's religious guidance; he might have wanted to kill him.

In its online magazine in April, ISIS listed Yusuf among 21 "obligatory targets" for its followers to "make an example of." It was the second time the terrorist group had threatened Yusuf's life.

Yusuf said he likely angered ISIS by preaching a sermon in 2014 in which he called them " stupid young boys. " More than 540,000 people have watched the sermon on YouTube in English, and many more in other languages.

ISIS' antipathy toward Yusuf goes beyond any one sermon. It also knows he is one of the few Muslim leaders with credibility to challenge its message to Western Muslims: You don't belong there. Come to the caliphate where you can live as a true Muslim.

"This revival of the Khilāfah gave each individual Muslim a concrete and tangible entity to satisfy his natural desire for belonging to something greater," ISIS said in a recent edition of Dabiq.

In the same edition, alongside interviews with ISIS fighters, articles praising "martyrs" and gruesome photos of its beheaded and burned victims, ISIS argued that Muslims in the West are living in a "grayzone."

The terrorists' goal is to divide the world into two camps: "the crusaders" and "the caliphate."

No Christians living in Muslim lands; no Muslims living in Christian countries. "Grayzones" are areas where Muslims practice their religion peacefully in non-Muslim countries. ISIS wants to eliminate these zones, in part by turning non-Muslims against their Muslim neighbors. Each terrorist attack chips away a little more grayzone, as Westerners marginalize Muslims, pushing them, ISIS hopes, into the caliphate's open arms.

"Muslims in the crusader countries will find themselves driven to abandon their homes for a place to live in the (caliphate), as the crusaders increase persecution against Muslims living in Western lands. ..."

Most American Muslims reject that message, but a few are inspired by it.

According to a study of 101 Americans charged with ISIS -related crimes, half were born in the country and most were citizens. Most were men under 30, one-third had converted to Islam. The vast majority expressed dissatisfaction with living in the United States, and 90% reportedly said they wanted to join the caliphate, perhaps heeding the call to surrender their lives to a larger cause, no matter how violent or quixotic.

"Overall, there is a sense of identity crises and alienation from society across a wide range of cases," the report says. "Anxieties over not fitting in, examples of personal isolation and social anger are frequent."

Those anxieties are often exacerbated, if not incited, by Islamophobia, said Sarah Lyons-Padilla, a social psychologist at Stanford University who has studied radicalization among young American Muslims.

American Muslims who felt hopeless, rejected and insignificant because of anti-Muslim discrimination were more willing to support extremist groups and causes, according to a study Lyons-Padilla led last year.

"ISIS would love to make all Muslims believe that the West is anti-Islam," the psychologist said. "When American politicians and citizens spread anti-Muslim rhetoric, be it through discriminatory policies or online trolling, they send the message that Muslims aren't 'real Americans' and that being Muslim is something to be ashamed of. In other words, they're basically helping ISIS recruit."

Counterterrorism officials agree.

In a recent Washington Post op-ed, retired US Army Gen. and former CIA Director David Petraeus said he has grown increasingly concerned about anti-Muslim rhetoric in the United States.

"As policy, these concepts are totally counterproductive," Petraeus said. "Rather than making our country safer, they will compound the already grave terrorist danger to our citizens. As ideas, they are toxic and, indeed, non-biodegradable -- a kind of poison that, once released into our body politic, is not easily expunged."

The number of American Muslims who radicalize is small, especially when compared with other Western countries, said William McCants, director of the Brookings Institution's Project on US Relations with the Islamic World

Law enforcement experts estimate that about 250 Americans have tried to join ISIS, far fewer than the thousands who have flocked to Syria and Iraq from countries such as France and Belgium.

"I would argue that American Islam is doing something right in contrast to these other countries," McCants said.

Most American Muslims are integrated and feel content with their lives, in sharp contrast with many Muslims in Western Europe, according to the 2011 Pew Center report . Nearly 90% speak English fluently, and more than 8 in 10 are citizens. Most say they see no conflict between being a devout Muslim and living in a modern society.

Still, 81 Muslim-Americans were associated with violent plots in 2015, the highest annual total since 9/11, according to the Triangle Center.

Omar Suleiman, a popular cleric who lives in Dallas, said he has sparred with young Muslims attracted to ISIS' black-and-white theology. Often, they are first- and second-generation immigrants who have grown up with some discrimination and "a whole lot of other-ness and awkwardness," he said. They are angry young men, frustrated with dead-end careers, irked by clerics who refuse to address controversial topics and incensed about the suffering of Muslims overseas in the Palestinian territories and Syria.

"When they find that people aren't addressing their concerns in an authentic way, they fall prey to Internet radicalism," Suleiman said. "They become disconnected from the mosque and disconnected from the American Muslim community."

A Donald Trump supporter holds up an anti-Muslim poster near the Republican National Convention in Cleveland in July.

Aleena's answer

Several months after submitting her letter to the President, Aleena received a call from the White House. Naturally, she thought it was a prank.

On the line was Asra Najam, who works in the White House Office of Presidential Correspondence. She said members of the Obama administration had read Aleena's letter and been touched by her honesty. Najam wanted to know if she could post it on the White House's Tumblr.

But there was another reason Najam was calling.

Najam's family emigrated from Pakistan when she was 4, moving to a Detroit suburb. She was 10 when the 9/11 attacks occurred. She remembers the comments people made about Islam in the aftermath, how she felt guilty just for being Muslim, how that feeling lingered for years.

"I was that 17-year-old-girl, like Aleena. I was lost, confused, unsure of how my identity fit into the broader American picture.

"But I definitely didn't have the courage to write the most powerful man on the planet about it," she said with a laugh.

Najam said she still struggles with her identity as an American Muslim, even though her desk looks out on the White House lawn, the country's most prestigious piece of real estate. She didn't know any Muslim women when she started looking for jobs in Washington, and she was terrified. Now she writes letters on behalf of the President.

Aleena's letter led to an invite to an Eid celebration in July at the White House, where she and Najam met in person. They snapped a picture in the ornate East Room and bonded over Adele, whom Aleena mentioned in her letter to the President.

Obama himself gave a short speech that afternoon , while Aleena, her mother and a family friend stood yards away, straining for a closer look among the 400 guests and the smartphones craned upward to record the moment.

As he had in his visit to the mosque in Baltimore, Obama praised American Muslims, calling them an "essential part of the fabric of our country."

But he also said he gets "heartbreaking" letters from American Muslims who tell him that they are anxious and afraid, especially now. He said he had a special message for the young people in the room: "We see you, we believe in you."

"And despite what you may sometimes hear, you've got to know that you're a valued part of the American family, and there's nothing that you cannot do."

It was an answer to Aleena's question: Which one am I allowed to be?

Both, the President said.

How can she be both? Aleena says that's a question she -- and all American Muslims -- have to answer for themselves.

She offers only one bit of advice: Speak up. You never know who might be listening.