Candan Badem teaches history at a university in southern Turkey, is a socialist and does not believe in God. But he lost his job and was hauled in by the police and accused of being a loyalist to a shadowy Islamic cleric who lives in exile in Pennsylvania.

The evidence against him: A book written by the cleric, Fethullah Gulen, was found in his office.

“It was like a bad joke,” said Mr. Badem, who says he believes the real reason he was targeted was that he signed a petition opposing the government’s war with Kurdish militants in the southeast. “What kind of reason can this be, for an academic to have a book? It is like the darkness of the medieval ages.”

Two months after a failed military coup, for which officials have blamed the disciples of Mr. Gulen, a wide-scale purge led by President Recep Tayyip Erdogan has reached witch-hunt proportions, according to a growing chorus of critics. More than 100,000 people — teachers, military officers, judges, functionaries, airline employees, even baklava salesmen — have been arrested or fired from their jobs, all on accusations of connections to Mr. Gulen, who steadfastly denies any involvement.

Mr. Gulen, 75, a moderate Islamist theologian who runs a network of schools and charities around the world, including in the United States, was once an ally of Mr. Erdogan’s before a bitter rift a few years ago. Now Mr. Erdogan calls him a terrorist.

In its early stages, the purge was supported by many of Mr. Erdogan’s opponents, who long chafed under what they called the president’s growing authoritarianism but who said that Mr. Gulen’s influence within society needed to be wiped out.

Now, though, many have turned against the president, saying that he is using the failed coup as a pretext for enhancing his own power and that he is wielding a state of emergency to target critics of all stripes, beyond the rule of law.

Fethullah Gulen at his home in Saylorsburg, Pa., in July. In Turkey, these days there are many ways to lose your job or land in jail: holding a mortgage from the bank affiliated with Mr. Gulen, current or past enrollment in one of the cleric’s many schools; simply owning a book or subscribing to a newspaper published by the Gulenists.CreditCharles Mostoller/Reuters

“After the coup, there was a moment of national unity, as Erdogan reached out to his secular opponents for reconciliation,” said Mustafa Akyol, a leading Turkish columnist who contributes opinion pieces to The New York Times and who initially supported the purges. “That was the hope. But now that spirit is increasingly fading, and there is justified worry that the purges may ultimately serve to cleanse the state of all critics, not just Gulenists who really seem to have masterminded the coup attempt.”

Alarmingly, to his critics, Mr. Erdogan has recently expanded the purge beyond even the pretense of going after Gulenists, removing Kurdish mayors and thousands of teachers in the southeast.

“He is openly purging the democratic society,” said Baskin Oran, a retired professor and prominent writer. “Anyone who opposes him. This is as clear as day.”

Mr. Oran said he lost his job in 1980, after a military coup and subsequent purge of leftists, but was eventually reinstated. “Even under martial law, I was able to go to court and get my job back,” he said. This time, under Mr. Erdogan, he said, the government wants its critics to “get out of the way for the rest of their lives.”

Turkish officials have lately acknowledged that they may have gone too far, and Prime Minister Binali Yildirim has said that crisis centers will be set up in every Turkish province to handle claims from those who feel they have been unfairly accused.

“If a mistake is made, if there is anything contrary to justice and the law, it will be reviewed after operations are completed and mistakes will be corrected,” he said in a televised speech.

But Mr. Erdogan and his subordinates have also been unapologetic about the severity of the purges, and they contend that most, if not all, of the people under suspicion for connections with the plot have been treated fairly.

“If anybody has any relations with this group of people who intended a coup d’état, we will never accept their excuses if we have enough evidence,” the deputy prime minister, Numan Kurtulmus, said in an interview with the New York Times editorial board on Sept. 7. Asked how thousands could be summarily dismissed before investigations had even begun, he said: “We obey the rule of law. The rule of law is still clear. After investigations, the courts will decide individual cases.”

In Turkey these days, there are many ways to lose your job or land in jail: holding a mortgage from the bank affiliated with Mr. Gulen; current or past enrollment in one of the cleric’s many schools; or simply owning a book or subscribing to a newspaper published by the Gulenists.

License plates with the letters FG, which might suggest an allegiance to Mr. Gulen, draw scrutiny from officials. The president has called on Turks to inform on their fellow citizens, and so the whispered word of a neighbor with a grudge could be enough to land someone in jail. So could a post on Twitter.

And if the police cannot find you, they may look for a family member. That happened in the case of Hakan Sukur, a former top soccer player who had fled to the United States, whose father was arrested. In another example, the wife of a journalist targeted by the government had her passport canceled.

Rather than focusing on people directly accused of participating in the coup plot, the purges have swept through the entire community of people who may have once been sympathetic to the ideas of Mr. Gulen.

That is no small number. A cleric who rose to prominence starting in the 1960s, Mr. Gulen has been embraced in the past by the West for espousing a vision of moderate Islam and interfaith dialogue. Gulenists have also long filled the ranks of the state — the police, judiciary and military — with the blessing of Mr. Erdogan.

While many of those who have lost their jobs, such as Mr. Badem, say they have never been sympathetic to the cleric, others readily acknowledge that they once considered themselves disciples of Mr. Gulen but say they had no role in the coup attempt.

Pelin Ozyurek, a 27-year-old schoolteacher, said she became acquainted with the Gulen movement in the same way many Turks did: by attending a private tutoring school, run by Gulenists, to prepare for her university entrance exams.

“That’s where I met the brothers and sisters of the movement,” she said in an interview. “It all started very innocently. They approached me and invited me to a picnic.”

She said that she had been persuaded in recent years to leave the movement by her husband and father, but that she still lost her job.

“I will never forget the day I was fired,” she said. “It was like someone poured boiling hot water over my head. The principal’s assistant told me by phone and made me pack up all my belongings in 20 minutes. I didn’t even get to say goodbye to the children.”

Ms. Ozyurek said that Mr. Erdogan’s Islamist government was being hypocritical, given the long alliance between his Justice and Development Party and the Gulenists.

“I am no guiltier than the government,” she said. “They were also sympathetic with the movement for many years.”

Searching for historical parallels, analysts have made comparisons with Joseph McCarthy’s anti-Communist witch hunt in 1950s America, the Stalinist purges of the 1930s and the Cultural Revolution in China in the 1960s and ’70s. Mr. Erdogan’s own spokesman, Ibrahim Kalin, has likened the purges to what a unified Germany did after the fall of the Berlin Wall in 1989 in removing civil servants and military officers who had served communist East Germany.