Just before the Fourth of July, Abdul El-Sayed, the son of Egyptian immigrants and a candidate for the U.S. Senate in Michigan, looked out at a few hundred people at a rally at a community college in Detroit and talked about the country’s momentous birthday.

“We’re on the cusp of our 250th anniversary,” he said.

“Boo,” someone scoffed from the front of the crowd, and Dr. El-Sayed stopped to make clear his disapproval.

“We don’t boo,” he said.

“I know the accident of history that allowed me to be born in this country,” he said. “I know what America can do for somebody. I just know that too often America does not do that for too many of her kids.”

Dr. El-Sayed, a former professor and public health official, is a uniquely important contender in a uniquely important race — generating equal parts enthusiasm and anxiety among Democrats with his populist message.

He is running for a must-win seat in the battle for control of the Senate, and Michigan’s Aug. 4 primary has become a critical front in the fight between Democrats’ progressive and moderate flanks and a pungent preview of the presidential primary to come.

He is campaigning on a sharply anti-Israel platform that also calls for abolishing ICE, raising taxes on the rich and making Medicare available to all Americans.

He is an establishment-accredited epidemiologist turned anti-establishment avatar.

And at a time when a growing number of Muslims are running for and winning political office, he would be the country’s first Muslim senator.

To his most ardent supporters, Dr. El-Sayed, 41, is a charismatic amalgam of Barack Obama and Bernie Sanders, a next-generation answer for a party and its ossified establishment whose more standard-issue standard-bearers lost twice to Donald Trump.

One of his aides calls him “Muslim Bruce Springsteen.”

To his critics, he is cocksure and condescending, a Rhodes scholar and Ivy Leaguer turned self-styled class warrior, a perpetual glory hound whose stances and statements have turned off some Black and Jewish voters.

They argue Dr. El-Sayed, if nothing else, is less electable than his more moderate primary opponent in a general election against Mike Rogers, the former Michigan congressman and presumptive Republican nominee.

“El-Sayed is a radical,” said Matt Bennett, a former staffer to President Bill Clinton and co-founder of the centrist think tank Third Way. Republicans agree.

But Dr. El-Sayed is more than a political lightning rod. He has lived his life, by chance and by choice, on the fault lines of the country’s complicated and contradictory record on matters of race, religion and immigration. He is an Egyptian American who was born and bred in Michigan, a onetime Kroger bag boy and high school football team captain who after Sept. 11, 2001, was called anti-Arab slurs like “raghead,” “towelhead” and worse.

He campaigns with a smile on his face but a chip on his shoulder. His rollicking oratory is laced with an edge.

“The lesson of the last 250 is, yes, America can correct,” Dr. El-Sayed said at the rally in Detroit, “if we’re willing to do the work of correcting her.”

He noted that the American Israel Public Affairs Committee, the pro-Israel lobbying group, is trying to beat him by shelling out tens of millions of dollars for ads for his opponent, Haley Stevens, a four-term congresswoman.

“They’re going to spend whatever it takes,” he told the crowd.

“I’m uppity and Arab, after all.”

‘Explaining myself since I was 3’

Early one recent morning in Ann Arbor, in the basement gym of his four-bedroom house, Dr. El-Sayed slid two 45-pound plates and a 25-pound plate on each side of the bar on the rack.

“I’ve been explaining myself since I was 3,” he said amid sets of squats. “Explaining who I was. Explaining why I looked the way I did. Explaining why my name was different.”

Abdulrahman Mohamed El-Sayed was born on Halloween in 1984 in Rochester Hills, Mich., north of Detroit. His first language was Arabic.

His parents divorced when he was a toddler. His mother remarried and moved abroad. His father married again, too, to a woman from Mid Michigan who had converted to Islam.

His father and stepmother were engineers who studied and taught at universities in Missouri, Florida and Michigan. His new grandparents were white Presbyterian deacons. “How are you my grandpa?” he once asked, his grandfather said in an interview.

His full first name was hard for other kids to say, and in 1989 Paula Abdul was a rock star and Kareem Abdul-Jabbar was a basketball star — and so in preschool in Columbia, Mo., Abdulrahman began going by just Abdul. In Arabic, Abdulrahman means “devotee of the Most Merciful.” Abdul means “devotee of” … blank.

He struggled and strived to fit in.

In elementary school in Kendall, Fla., he brought Middle Eastern pita with ful, a fava paste, for lunch. Classmates, he said, teased him for eating “a turd sandwich.”

In middle and high school in woodsy, well-to-do Bloomfield Township, Mich., where he estimated Muslims made up about 5 percent of his classes, he wore JNCO jeans and listened to Tupac Shakur. He scooped ice cream at Cold Stone Creamery and wrestled and played football. He craved pizza more than kofta.

He was raised mostly by his father and stepmother. In his blended family, with two sets of half siblings, one set half-Palestinian, the other half-white, he was the only full Egyptian in his generation.

His father demanded nothing less than A grades. He had to clean the kitchen every night.

One night when he was 16, he said he was going to pray at his family’s mosque but instead sneaked out with friends — and was picked up by the police for violating a local curfew. “What are you doing in this part of town?” an officer said, according to his recollection. They took him home in handcuffs, and his father, in his galabia, a long, loose North African robe, opened the door.

“I wanted to be loved,” he wrote in his memoir. “I tried to explain, but Baba was already halfway up the stairs. The only thing my father ever said was that he was disappointed.”

Three weeks later was 9/11. On the football field, from the stands and around town, he said, he heard a new kind of hate. Damn Muslims. Go back to your country. Get out of here, Osama — the name of his younger brother.

In 2003, he went to the University of Michigan, where he met the woman who would become his wife. In Sarah Jukaku, a Muslim whose parents emigrated from India, he sensed what he sought.

“Sarah had the quiet confidence of someone who had known love unconditionally,” as he put it in his book. “She didn’t need to explain, prove or justify herself.”

Back in his basement, done with his squats, he used a chain to strap a 45-pound plate to the belt on his waist and did pull-ups, one, two, 10, the only sound in the gym the whir of a fan and the huff of his breath.

‘Dear Abdul …’

In a tight, black V-neck T-shirt, Dr. El-Sayed ran into the auditorium of the First Unitarian Universalist Congregation of Ann Arbor one recent afternoon, hugging and high-fiving people in the crowd. He jumped onto the stage and started his speech with a boisterous call-and-response.

“Money out of …”

“Politics!” people shouted.

“Money in your …”

“Pocket!”

“Medicare for …”

“All!”

“You know, it helps to have a message that people remember,” he said. “That way, you might not have to have $23 million of AIPAC spending for you.” He did not name Ms. Stevens because he didn’t have to. He laughed, and the crowd did, too.

“I got a name that’s got 11 letters in it — sounds that come out of parts of people’s throats most people don’t know they have,” he said. “People like me are not supposed to run.”

At the University of Michigan, Dr. El-Sayed was active in the Muslim Students’ Association. He played club lacrosse and protested the war in Iraq, he said, by choosing not to face the American flag during the national anthem. He graduated with highest distinction, according to the university, with degrees in biology and political science.

As the student speaker at his commencement in the spring of 2007, he urged his classmates to have “the audacity to believe that we can change this world.” The main speaker told him he “had a natural gift for speaking,” he recalled, suggesting that someday he should run for office, even though he was headed to medical school.

“Dear Abdul,” the main speaker, Bill Clinton, wrote to him in a note dated three days later. “Your commencement speech was terrific — I wish you well and will try to live long enough to need you as my doctor.”

He did two years of med school at Michigan, followed by two years as a Rhodes scholar at Oxford. A professor there told him he was the most American person he knew — a descendant of immigrants in a nation of immigrants, and confident to the point of brash. He got a doctorate in epidemiology from Oxford and continued med school at Columbia and got a medical degree. But he soured on the health care system during the clinical portion of his training, he said, convinced it was designed more to profit off sick people than to make them well. Instead of a practicing physician, he became a tenure-track professor.

Now, back at the lectern at the Unitarian church in Ann Arbor, Dr. El-Sayed was still talking about AIPAC.

“You’ve been seeing their ads up and down your TV screen,” he told the crowd.

“Shame!” people yelled.

He slapped the lectern and leaned back and laughed.

“Money can’t buy you a message,” he said. “Money can’t buy you the truth. Money can’t buy you the people.”

The people hollered and cheered.

“Money,” he said, teeing up another dig at the folksy Ms. Stevens, “can’t even buy you a personality.”

‘Look up, not down’

“Almost there. Almost there. Almost there.”

He has two daughters. The elder is Emmalee, whose name means “my hope” in Arabic. When she was born, he read the Muslim call to prayer into her ear, as per custom. Allahu Akbar, Allahu Akbar. Ash-hadu an la ilaha illa Allah. Now, in a rock gym in Madison Heights, outside Detroit, he watched her climb.

“Look up, not down,” he told her.

“Look up,” he said.

Dr. El-Sayed was 30 when he was named executive director of the Detroit Health Department. He worked for a year and a half in the $165,000-a-year job and tried, with up-and-down results, to rid schools of lead and restructure a mismanaged animal shelter. He partnered with a Los Angeles-based nonprofit called Vision to Learn, putting glasses on the faces of needy kids — and at times taking undue credit, detractors claim, by saying he “built” and “created” the program.

He resigned to run for governor in 2018 — a political novice who championed Medicare for all and earned the endorsements of Mr. Sanders and an up-and-coming Ms. Ocasio-Cortez — and lost, by more than 20 points, to Gretchen Whitmer, the current governor (who on Friday endorsed Ms. Stevens).

After his defeat, Dr. El-Sayed became a visiting professor at Michigan, a scholar-in-residence at American University and at Wayne State University, and a fellow at the University of Chicago Institute of Politics.

He co-hosted a podcast for Crooked Media, founded by former aides to Mr. Obama. He was a commentator for CNN. He started his own media and production company and political action committee.

He co-wrote a book promoting universal health care, saying Medicare for all “would signify a decisive break with the past 40 years of our politics.” And he wrote “Healing Politics,” part memoir, part manifesto, in which he described Mr. Obama’s presidency in part as “inspiring intentions unfulfilled.”

For two and a half years, he was the director of the health department of Wayne County, Mich., where he put free Narcan in vending machines, worked to improve a troubled juvenile detention facility (although he overstated the extent to which he did, according to The Detroit News) and erased citizens’ medical debt (by about $60 million, not the $700 million he and his campaign have suggested, according to Bridge Michigan and The Detroit Free Press).

He resigned last year to run for the Senate.

Back at the rock gym, his daughter kept going.

“I can’t do this,” she said.

“Yes, you can,” he said.

“Yes, you can. Yes, you can. Yes, you can.”

A test for Democrats

North of Detroit, in liberal, suburban Ferndale one recent evening, Dr. El-Sayed ran into the sweaty, stuffy basement of the First United Methodist Church. Mr. Shakur’s “Changes” blared as he bounded onto the stage.

“The establishment’s taken to calling me dangerous,” he said.

“They’re scared!” a man sneered.

“The people who got debt elimination letters — do they think I’m dangerous?” Dr. El-Sayed said. “What about the kids who are wearing glasses and can see the blackboard?” he said.

“I’m not dangerous if you’re someone who needs government to work for you,” he said.

“But if you’re Chuck Schumer,” he said, referring to the Senate Democratic leader, who has privately told donors he prefers Ms. Stevens, “damn right I’m dangerous!”

For more than a year, the Michigan Senate campaign was a three-way test case of Democrats’ warring ideological tracks — Dr. El-Sayed (progressive), Ms. Stevens (moderate) and State Senator Mallory McMorrow (the dwindling space in between). Ms. McMorrow ended her bid a few weeks back. Now the choice is all the more stark. It’s gotten ugly.

“I hope maybe they find some way to teach her how to string together two coherent sentences,” Dr. El-Sayed said of Ms. Stevens in a recent interview with Semafor (not long before he told “people online” to stop being “unkind”). “When you sell out for that many corporations and special interests, I guess you forget how to think for yourself.”

In a statement to The New York Times, Ms. Stevens dismissed Dr. El-Sayed as a wannabe “celebrity senator who seems more interested in getting on a podcast or going viral than he does about putting his head down and doing the work for Michigan.”

“He’s never won an election,” Ms. McMorrow said in an interview before she dropped out.

Polls say he has a chance to win this one.

“The tectonic plates of the entire Democratic Party will be on a path to moving in a major way if he wins the primary and the general election, setting things up on a much more bold and economic populist path,” said Adam Green, a co-founder of the Progressive Change Campaign Committee. “This is a chips-on-the-table moment.”

Buoyed by white, college-educated and younger, disaffected voters, and endorsed by the United Automobile Workers, the Working Families Party and End Citizens United, Dr. El-Sayed has rallied with progressive luminaries like Mr. Sanders and Ms. Ocasio-Cortez and Representatives Ro Khanna and Rashida Tlaib. He has campaigned with Hasan Piker, the anti-Zionist, Marxist streamer. He has called Israel’s government “evil” and its actions in Gaza a “genocide.”

He denounced an attack this spring by a Muslim Arab American on a Jewish synagogue in West Bloomfield Township — but qualified his condemnation in a way that made some balk. “Hurt people hurt people,” he said.

Republicans have already signaled how they’ll run against him. They’ll call him a socialist, a label he rejects. And they’ll use his whole name: The same way they ran against Barack Hussein Obama, they’ll run against Abdulrahman Mohamed El-Sayed.

In Ferndale, the basement of the Methodist church was steamy and standing room only. People used campaign fliers as hand-held fans.

Onstage, Dr. El-Sayed held court.

He talked about his grandparents, his parents and his children. He talked again about the 250th anniversary, “the sins of this country” and its “sordid history.” He talked about what it has been and what it could be.

“We hold these truths to be self-evident, that all men — it should say ‘people’ — are created equal, government of the people, by the people and for the people,” he said. “And so it’s on us to decide.”