Michael R. Bloomberg is a former Wall Street mogul with a passion for the rights of a private property owner. He is a Jew whose parents asked their Christian lawyer to buy a house and then sell it back to them to hide their identity in an unwelcoming Massachusetts suburb. And he is a politician who regards his independence as his greatest virtue.
That potent combination of beliefs and history, those closest to Mayor Bloomberg say, has fueled his defense of the proposed Muslim community center in Lower Manhattan — a defense he has mounted with emotion, with strikingly strong language and in the face of polls suggesting that most New Yorkers disagree with him.
"Something about this issue just really hooked into him," said Howard J. Rubenstein, the powerful public relations executive, who is a friend of Mr. Bloomberg. "It deeply upset him."
Mr. Bloomberg's forcefulness has won him new admirers, but also a chorus of both familiar and fresh detractors. Reliable newspaper editorial allies have turned against him. Conservative pundits have mocked him (one called him "self-deluding"). Even some of his closest friends have angrily differed with him.
City Hall officials, who said the mayor had been swamped with angry correspondence, made some of it public.
"You are going to allow the Muslims build a trophy building there on HOLY GROUND," one e-mail read. It concluded: "You need to be impeached."
But none of the anger — hard to measure precisely, and amplified by talk radio and cable television — has moved the mayor. Indeed, interviews with his aides, advisers and associates suggest that it has only strengthened his resolve.
And they say the reasons are civic and personal. Mr. Bloomberg, for instance, has come to know the husband and wife who are among the principals behind the proposed center — a multipurpose religious and cultural institution that would be built two blocks from the site of the World Trade Center.
And for years he has, with a mix of care and impatience, been encouraging New Yorkers, including the families of 9/11 victims, to emotionally move beyond the tragedy of nine years ago.
Some of those impressed by the depth of Mr. Bloomberg's feelings have been struck in part because he had disappointed many when, by their lights, he failed to stand behind the principal of the city's first Arabic-language public school.
The case of the principal, Debbie Almontaser, began, much as the community center did, with a seemingly uncontroversial plan — a school that would teach Arabic. Soon enough, though, conservative advocates, inflamed by the proposal, branded Ms. Almontaser a "radical" and "jihadist."
After opponents sought to link her to T-shirts that said "Intifada NYC" and a newspaper suggested she had defended the slogan, the Bloomberg administration forced her to resign in 2007, she said.
A federal employment commission determined that Ms. Almontaser had not been connected to the T-shirts, that the newspaper had misconstrued her words and that the Bloomberg administration "had succumbed to the very bias that creation of the school was intended to dispel." (The school has survived and is run by a new principal.)
Now, some Muslim leaders in New York express pleasant surprise at his position on the downtown center.
Robina Niaz, executive director of the Muslim social service group Turning Point for Women and Families, said his position in the Almontaser case "was totally the opposite, completely the reverse of this."
Her sense, she added, was that Mr. Bloomberg "may have gone back and looked at how that was not helpful as a mayor, as a leader — that this was an opportunity to undo some of that."
On the community center, Mr. Bloomberg's thinking from the start was informed by what he describes as the basic rights of the people behind it.
"If somebody wants to build a mosque in a place where it's zoned for it and they can raise the money, then they can do that," he said. "And it's not the government's business."
Mr. Bloomberg, it turned out, had met with the couple seeking to build the center. Imam Feisal Abdul Rauf, the imam who would run the center, led a prayer service at Gracie Mansion in 2009 and exchanged warm words with Mr. Bloomberg; his wife, Daisy Khan, had sat next to Mr. Bloomberg's girlfriend, Diana L. Taylor, during a dinner that followed.
In early summer, as controversy started to swirl around the project, opponents began to raise questions about Islam itself, suggesting that it has tolerated radical elements, and hinted that the planned center could inspire acts of terror in the United States.
Those claims infuriated Mr. Bloomberg, in no small part, those close to him say, because of his own family's brush with prejudice when his parents shielded their identity from the seller of their house in Medford, Mass., a town where entire neighborhoods were still off limits to Jews.
Mr. Bloomberg's instinctive discomfort with the nature and tenor of the growing debate about the center moved him to seek the counsel of others he trusted.
A few weeks ago, he approached an adviser on Muslim issues, Fatima A. Shama, a Palestinian-American who is his commissioner of immigrant affairs. He asked what she thought of the project.
Ms. Shama framed the issue in personal terms: she has three sons, she told the mayor, but there is no place in the city for them to share their Muslim faith with their Jewish and Christian friends.
"This could be that place," Ms. Shama told Mr. Bloomberg.
The future of the center at that moment hinged on a decision by the city's Landmarks Preservation Commission.
If it voted to prohibit alterations to the building on the site on Park Place, the developer's plan would come apart.
In mid-July, Mr. Bloomberg made a quiet trip to the site, a forlorn former clothing store two blocks from City Hall. He saw no features that he considered worthy of landmark designation .
"It's pretty hard to argue it should be preserved the way it is," he said.
With a decision looming, state and national politicians began to weigh in, attacking the center as an act of aggression against American values.
In a widely watched address, Newt Gingrich, a former House speaker who has worked with the mayor on education reform, criticized the planned center and encouraged Mr. Bloomberg to change his mind.
But Mr. Bloomberg was heartened to hear that some of the families of 9/11 victims supported his position; they told him so a few weeks ago at a fund-raiser for the memorial at the site.
"One hundred percent of them in the room kept saying, 'Please keep it up, keep it up,' " he recounted. " 'Our relatives would have wanted this country and this city to follow and actually practice what we preach and what we believe in.' "
Mr. Bloomberg became even more determined to speak out after he learned that the Anti-Defamation League, which for weeks has denounced what it saw as bigoted attacks on the Muslim center, abruptly announced its opposition. He was surprised and disappointed.
When asked about the group's position, the mayor called it "totally out of character with its stated mission."
In a pointed jab, he added, "I have no idea what possessed them to reach that conclusion."
He asked his aides to draft a speech that would not only explain his position, but would also forcefully rebut the project's critics and reframe the debate.
On Aug. 3, a few hours before the speech was to be delivered, his top speechwriter, Francis Barry, showed the mayor the text.
"It's not nearly strong enough," Mr. Bloomberg said, Mr. Barry recalled.
The mayor inserted his own language, citing the firefighters and police officers who marched into the trade center on Sept. 11: "In rushing into those burning buildings, not one of them asked, 'What God do you pray to?' 'What beliefs do you hold?' "
And he proposed what would become the speech's defining lines: "We do not honor their lives by denying the very Constitutional rights they died protecting. We honor their lives by defending those rights — and the freedoms that the terrorists attacked."
His steadfast support for the center, and his denunciation of its outspoken opponents, have put him at odds with some longtime friends, like Michael H. Steinhardt, a financier and philanthropist for Jewish causes.
"I disagree with him, respectfully," Mr. Steinhardt said. He found the tone of some of the mayor's remarks, especially the statement that opponents of the project "should be ashamed of themselves," to be "somewhat puzzling," Mr. Steinhardt said in an interview.
Nor has it endeared the mayor to a certain number of New Yorkers who have made their disappointment clear in letters and e-mails to City Hall.
One writer said she had been prepared to support a potential Bloomberg presidential campaign. "But not now," she wrote. "This has totally changed my opinion of the mayor."
There were also letters of praise. A woman who fled Lower Manhattan on Sept. 11 thanked the mayor for his courage. Another letter-writer called it "his finest moment as mayor."
Faced with the response, the mayor told aides he would not change his mind, but the aides say he has seemed sensitive to the raw emotions that the issue has aroused — especially toward him.
"I have said it so many times I'm getting tired of it," Mr. Bloomberg said recently of his support for the center. Then he continued, in something of a lament: "I'm not winning a lot of friends doing so."