So much for President Erdogan’s blurred vision of fashioning an Ottoman Empire 2.0. With the king-sized drubbing he took in local elections on Sunday, Turkey’s autocratic leader may already be facing the future as a footnote. 

That comes as good news for his numerous critics both inside and outside Turkey, a strategic and strong country that is nevertheless economically reeling and perennially problematic when it comes to freedom of the press and expression of dissent. 

The 70-year-old Mr. Erdogan’s neo-Ottoman Justice and Development Party, or AKP, lost out in a big way to the opposition Republican People’s Party, or CHP, a social-democratic party founded by Atatürk. It is a slap inflicted on the Turkish president who was personally invested in a highly publicized campaign.

At his party’s Ankara headquarters on Sunday night Mr. Erdogan told his supporters that his party suffered a “loss of altitude” but that he would respect “the decision of the nation.” Mr. Erdogan’s loss of altitude is secular Turkey’s gain. With 99 percent of ballots counted, the Republican People’s Party rode to victory at mighty Istanbul and at Ankara.

At the Turkish capital the incumbent CHP mayor, Mansur Yavas, did not even wait for the official results, which will be communicated on Monday, to proclaim himself the winner and declare that “those who were ignored” sent a clear message “to those who run this country.” Mr. Yavas looked set to keep his seat with a stunning 25-point difference over his challenger.

At Turkey’s showcase city, Istanbul, the incumbent mayor, Ekrem Imamoglu, looked set to keep his seat at the head of the city he has led since 2019. The moderate 52-year-old Mr. Imamoglu has locked horns with Mr. Erdogan in the past and is seen as his rival. It was the AKP that held sway by the Bosphorus until Mr. Imamoglu, a real estate developer by trade, came along in March 2019.

As of this April his political future holds some unmistakable spring promise, and the much-beloved mayor of Istanbul has now placed himself in a favorable position for the 2028 presidential election.

Mr. Imamoglu won slightly more than half of the votes at Istanbul, while AKP candidate Murat Kurum trailed by about ten percent. Now, Mr. Imamoglu’s unmistakable momentum is veering into swagger. To thunderous applause at a large Istanbul city square, Mr. Imamoglu said, or shouted rather, that “the 16 million people of this city have won — women, young people, Kurds, Christians, Syrians, Jews, and people of all beliefs have won!” 

Following that declaration the crowd asked him to remove his jacket and tie, a gesture that he now makes at virtually all of his rallies. He complied, saying above the din, “Today is a message for President Erdogan and for the government. Money must now be spent on the people, no more waste.”

This comes as comeuppance for the humorless Mr. Erdogan, whose political career kicked off as mayor of Istanbul in 1994. In the past he has said that “whoever governs Istanbul, governs Turkey.”

According to Turkish press agency Anadolu, the CHP won the municipalities of 36 of Turkey’s 81 provinces, making inroads into many strongholds of Mr. Erdogan’s party. It garnered 37 percent of the votes nationwide, compared to 36 percent for the AKP. 

These are election results without precedent in Turkey, particularly in the Anatolia region where the CHP conquered municipalities long held by the presidential party. It is the CHP’s biggest electoral victory since Mr. Erdogan, who is at least publicly a harsh critic of Israel, came to power two decades ago.

“Today, the voters decided to change the 22-year-old picture in Turkey and open the door to a new political climate in our country,” declared a pharmacist who also chairs the CHP, Özgür Özel.  

This is all the more remarkable for Mr. Erdogan because he benefited from a much more extensive campaign than his competitors, with a ubiquitous press presence in the runup to Sunday’s vote.

The AKP did maintain its candidates in other large cities in Anatolia, such as Kayseri and Erzurum. The pro-Kurdish DEM party rose to the top of several cities in the southeast, notably in Diyarbakir, the largest Kurdish-majority city in Turkey. The CHP was leading in another major city, Izmir, and everywhere else along Turkey’s long Aegean and Mediterranean coast. 

The square where Mr. Imamoglu spoke Sunday night at Fatih is a traditionally Islamic neighborhood and stronghold of the AKP. Yet the Turkish times, they are a changin’: as the popular mayor took to the stage, television cameras captured from the ecstatic crowd  multiple chants of “Erdogan, resign.”