Over the past few years, Mr. Erdogan had begun alienating his liberal supporters by intimidating the news media and pursuing large urban development projects without public feedback. Then in recent weeks a group of protesters trying to save a city park from demolition were met with a fierce police response, setting off the larger antigovernment street movement that challenged Mr. Erdogan, whose response to the crisis confirmed for many of his former supporters that he had taken a path they could no longer support.

Beyond his democratic promises, many experts say Mr. Erdogan’s charisma won over many liberals years ago.

Jenny B. White, an anthropologist at Boston University, spent time in Turkey in the 1990s researching the rise of Islamist movements, and followed Mr. Erdogan around while he was mayor of Istanbul.

“He would ignore a table of bearded mayors after an event and talk to me like I was the only person in the world,” she said. “There is that aspect of it that really captured people.”

She added, “The liberals voted for him because when he was elected in 2002 he did all these things liberals only dreamed of.”

Not all on the left have broken with Mr. Erdogan. Nursuna Memecan, a member of Parliament from the A.K.P. who is close to Mr. Erdogan and identifies herself as a liberal, said she helped arrange meetings between some of the protest leaders and Mr. Erdogan in hope of brokering a compromise, and winning back some of his former supporters. That did not happen, though, as a tentative deal to save the park was disavowed by most protesters, and Mr. Erdogan ordered a decisive police raid on Saturday to clear the park.

Referring to Mr. Erdogan’s rise to power, Ms. Memecan said: “The real liberals supported him. They had no prejudices against him or his religion or what class he came from. His piousness did not bother them.”