His supporters see him as a modernizer and reformer (he got a green card as an exceptional educator). His foundations promote warm relations with other religions (he has apologized for anti-Semitic remarks made many years ago). And he is a strong proponent of Turkey becoming part of the European Union.
However, his detractors critique him and his movement as secretive and cultish, and claim he controls a shadowy network of supporters in the Turkish security services and bureaucracy that has a hidden agenda. (That "opaqueness," claims Alp Aslandogan, head of the Gülenist Alliance for Shared Values, is due to Turkish political culture, which long branded anyone who did not subscribe to secular "Kemalism" as an internal enemy.)
Whatever its reasons, the nontransparency of the Hizmet network arouses suspicions (including an FBI investigation of some of its schools for possible money skimming, and the pending closure of another school in Philadelphia). And Hizmet's secrecy makes it vulnerable to Erdogan's attack.
Ironically, Erdogan and Gülen were allies for years in a joint effort to subordinate the coup-prone Turkish military to civilian control. This was a cause in which Gülen supporters in the police, judiciary, intelligence services, and press were extremely active. Neither Erdogan, whose party has roots in Islam, nor the Gülenists showed any concern for the nontransparency of show trials against generals, secular educators, and journalists. Known as Ergenekon and Sledgehammer, these trials were based on shaky evidence and doctored wiretaps and sent innocent people to jail.
But the two men have recently fallen out over democracy and corruption. Judged by his principles, Gülen seems the more democratic. When it comes to methods, however, the verdict is out.
Gülen angered Erdogan when he criticized the prime minister's crackdown on environmental protesters last year, which sparked huge national demonstrations. The scholar rightly labeled the crackdown undemocratic. Score one for Gülen.
The two men finally parted ways over corruption. Erdogan blamed Gülen supporters inside the police and judiciary for bringing graft charges (and leaking incriminating tapes) against several cabinet ministers and against his own son, in the run-up to recent municipal elections.
Gülen was unrepentant. "If among those who conducted the graft investigations were some people who might be connected to the Hizmet movement, was I supposed to tell [them], 'Turn a blind eye'? Did they expect me to do this?" he told the pro-Gülen newspaper Today's Zaman.
The problem lies not in prosecution of corruption, however, but in the tactics - leaked tapes with heavy coverage by pro-Gülen media. Gülenists, of course, deny doing any leaking. As for Erdogan, he supported such tactics in the Ergenekon trials, but decries them when they hit home.
Why should Americans care about this dispute? Because Turkey matters. A rising economic power (give credit to Erdogan), it could become the first predominantly Muslim country to successfully meld Islamic values with pluralistic politics. And it belongs to NATO.
Yet Erdogan is using the fight with Gülen as an excuse to exert semi-authoritarian control over key areas of government. He has gutted large segments of the police and judiciary, removing or transferring thousands of supposed Gülen supporters, and is taking tighter personal control of the intelligence services.
With elections over, Erdogan has pledged that the Gülenists "will pay the price" for their supposed leaks. Erdogan's party won a plurality by playing the victim, and blaming the Gülenists for slander; he is likely to continue this game.
Indeed, Erdogan is now using Gülen as an excuse to crush social media. After blaming a new leak from the foreign ministry on Hizmet, the prime minister blocked YouTube and banned Twitter (the country's highest court reversed the ban Thursday). He is trying to censor the Internet.
And the Turkish leader has asked President Obama to take action against Gülen, saying, "The person who is responsible for the unrest in Turkey lives . . . in Pennsylvania. You have to take the necessary stance." The White House denied Erdogan's claim that Obama reacted "positively" to his request for action on Gülen.
Sadly, this battle is not about modernizing Islam or about building better democratic institutions. Instead, it pits an elected leader with an authoritarian bent against an Islamic scholar with appealing ideas but secretive, suspect methods.
I'd like to ask "the man from Pennsylvania" about his intentions, but so far, have not been granted one of his rare interviews. As Erdogan goes on the offensive, Gülen should lift the veil of secrecy from his organization. Transparency may be his best defense.
WORLDVIEW | TRUDY RUBIN