IZMIR, Turkey — Stabbing the air with his finger, Muharrem Ince strides along the roof of his campaign bus and tells a provincial crowd that the fortune President Recep Tayyip Erdogan spent on his new palace in Ankara could have built 100,000 houses.

“And now he’s building a summer palace of 300 rooms in Marmaris,” Ince adds, provoking a loud boo from the crowd in Kemalpasa, western Turkey.

Turkey has all the resources it needs, Ince says. “We’ve got the flour, the butter, the sugar, but we cannot make helva [a sweetmeat] because the chef is stealing the flour.” The people roar. They know who he means by “the chef.” And they are confident that Ince — the candidate of the main opposition Republican People’s Party (CHP), the torchbearer of secularism in Turkey — is the man to vote for to end Erdogan’s 15-year rule.

When the campaign for the June 24 polls began in mid-April, this cheerful former teacher was a middle-ranked politician who was forecast to place a distant third in the presidential race behind Erdogan and his popular female challenger, Meral Aksener.