ISTANBUL -- In building his political career, Turkey's powerful and charismatic Prime Minister Recep Tayyip Erdogan relied heavily on the support of a Sufi mystic preacher whose base of operations is now in eastern Pennsylvania.
The two combined forces in an epic battle with the nation's secular military elite, sending them back to the barracks in recent years and establishing Turkey as a successful example of moderate, democratic Islamic government.
Now, a corruption scandal not only threatens Mr. Erdogan's rule, but also has exposed a deepening rift between the prime minister and his erstwhile ally's followers that is tearing the government apart.
On Thursday, after several days of sensational disclosures of corruption in Mr. Erdogan's inner circle, Istanbul's police chief was dismissed, as the government carried out what officials indicated was a purge of police and officials conducting the corruption investigation -- nearly three dozen so far, according to the semi-official Anadolu news agency.
Repeating much the same strategy he employed as he battled thousands of mostly liberal and secular-minded anti-government protesters last summer over a development project in a beloved Istanbul park, Mr. Erdogan is portraying himself as fighting a "criminal gang" with links abroad.
That is an apparent reference to Fethullah Gulen, an imam living in Saylorsburg, Pa., in Monroe County north of Allentown, who adheres to a mystical brand of Sufi Islam and whose followers are said to occupy key positions in Turkey's national government, including the police and judiciary, but also in education, the news media and business.
Mr. Erdogan weathered the summer of protest, emerging with his base's support even as his image abroad was tarnished. But the corruption inquiry poses a challenge that analysts and some Western diplomats believe could be even greater. It has ensnared several businessmen close to him, including one major construction tycoon, the sons of ministers and other government workers involved in zoning and public construction projects.
Mr. Erdogan and Mr. Gulen have disagreed on various important issues in recent years, although the tensions were previously kept largely silent.
Mr. Gulen was said to have opposed the government's activist foreign policy in the Middle East, especially its support for Syria's rebels. He is also said to be more sympathetic to Israel, and tensions flared after the Mavi Marmara incident in 2010. That was when Israeli troops boarded a Turkish ship carrying aid for Gaza and killed eight Turks and one American of Turkish descent, leading eventually to a rupture in relations -- since patched up -- between Turkey and its one-time ally.
The escalating political crisis, experts say, underscores the power Mr. Gulen has accumulated in the Turkish state that threatens to divide Mr. Erdogan's core constituency of religious conservatives ahead of elections in the next 18 months.
Mr. Gulen left Turkey in 1999 after being accused by the then-secular government of plotting to establish an Islamic state. He has since been exonerated of that charge and is free to return to Turkey, but never has.
He lives quietly in Pennsylvania, though followers are involved in an array of businesses and organizations in the United States and abroad.
Huseyin Gulerce, personally close to Mr. Gulen and a writer for a Gulen-affiliated newspaper, said his followers have many of the same complaints about Mr. Erdogan as did protesters this summer. They think the prime minister has become too powerful, too authoritarian, and has abandoned his earlier platform of democratic reforms.