Turkey’s President Amassed Power. He Could Still Lose This Election.

Overseeing Sunday’s vote is the Supreme Election Council, a panel of judges. For decades, it was widely regarded as independent and trustworthy, but two recent decisions marred its reputation in the eyes of opposition supporters.

In 2017, while the votes were being counted in a referendum on changing Turkey from a parliamentary to a presidential system, the board decided to override the electoral law and include ballots that lacked an official stamp proving their authenticity. The referendum passed by a slim margin, allowing Mr. Erdogan, the president at the time, to greatly expand his powers.

In 2019, after an opposition candidate beat Mr. Erdogan’s candidate in the mayor’s race for Istanbul, Turkey’s largest city, the council voided the results, citing irregularities, and called for a redo. The same opposition candidate won that, too, by an even larger margin.

Those decisions raised questions about the election board’s willingness to rule against Mr. Erdogan’s preferred outcome, said Hasan Sinar, an associate professor of criminal law at Altinbas University in Istanbul.

“On paper, they are neutral,” he said. “But when the government stays in power so long, no one in that position can be neutral anymore.” Any doubt about the electoral board’s neutrality was detrimental to Turkey’s democracy, he added. “This is never supposed to be poisoned by doubt,” he said.

In recent weeks, Mr. Erdogan has used his bully pulpit to bludgeon the opposition, warning that the country would suffer under their leadership and accusing them of conspiring with terrorists. Mr. Erdogan’s interior minister, Suleyman Soylu, who oversees the security forces, has gone further, sowing doubts about the results before the vote even begins.