ISTANBUL—As Turks head back to the polls this weekend for a rerun of the election that rejected President Recep Tayyip Erdogan’s bid to consolidate power, the country’s fortunes have taken a turn for the worse.

Turkey’s government, unable to form a coalition after weeks of talks, is paralyzed by partisan divisions. The economic malaise is deepening. The military is embroiled in an expanding conflict with Kurdish militants and Islamic State forces. And the country’s capital, Ankara, has been shaken by a recent terrorist attack—the deadliest in the nation’s history—that some have called “Turkey’s 9/11.”

Mr. Erdogan has responded to his country’s crises with a high-risk gamble: another round of parliamentary elections, to be held Sunday, that he hopes will restore his once-unchallenged grip on the government.

The vote is being closely watched by world leaders who are counting on Turkey to play a bigger role in choking off the flood of Middle East refugees and to combat Islamic State. At home, its own citizens are looking to their government to prevent Islamic State suicide bombers and Kurdish militants from stepping up their deadly attacks.

The shift against Mr. Erdogan became clear in June, when his Justice and Development Party, or AKP, fell 18 seats short of the 276 needed to form a government on its own. Voters brought an unexpected end to the AKP’s control by electing larger numbers of lawmakers who opposed Mr. Erdogan’s bid to boost his presidential power.

The AKP has rolled out a new campaign that party officials say is meant to persuade voters that it got the message they delivered in June—and that it is willing to do things differently.

It is promising to raise the minimum wage, cut taxes on farmers and ranchers and boost retirement payments, while redoubling the country’s efforts to fight terrorism. The party’s slogan, on signs plastered on campaign buses across the country, reads: With the passion of the first day.

Days before the vote, however, the most recent polls suggest that the new message doesn’t appear to be resonating with enough voters to restore the party’s absolute majority position in parliament. An average of recent polls calculated by Turkey’s Deniz Investment shows the AKP winning 265 seats in the 550-member parliament, 11 short of the lawmakers it would need to rule without sharing power.

Mr. Erdogan’s aides declined to comment on the election and didn’t respond to requests for interviews.

With Sunday’s vote expected to create another divided parliament, the shaky footing of a weak coalition government could pave the way for months, if not years, of political instability. Another inconclusive election is expected to put pressure on Mr. Erdogan to embrace a power-sharing deal with bitter rivals who have worked for years to undermine the president’s political agenda.

“Turkey is at a very unique juncture for a democracy,” said Soner Cagaptay, director of the Turkish Research Program at the Washington Institute for Near East Policy. “What happens if Erdogan loses? What game does he play?”

A few short years ago, Mr. Erdogan was firmly in control of Turkey’s future and on a glidepath to bring the long-emerging market into the mainstream, buttressed by a surging economy and goodwill from the West.

The AKP controlled parliament beginning in 2003, after riding to power in 2002 by winning support from voters across the political spectrum, including some Kurdish supporters, liberal allies and its conservative religious base.

Turkey’s fortunes began to rise as Mr. Erdogan led the country into a new era of economic growth that made it one of the world’s most promising emerging markets, creating more momentum for its ambitions to join the European Union. But AKP support began to erode as the economy stalled, incomes fell, and talks about joining the EU stalled.

A sense of disillusionment spread as Mr. Erdogan and top government leaders consolidated power and sought to marginalize rivals.

Mr. Erdogan and his key allies have been denounced for arresting critics in the media, and castigated for embracing a more uncompromising conservative religious agenda that alienated more liberal members of the party. The AKP has also been hobbled by a politically charged government corruption investigation that Mr. Erdogan has decried as the work of rivals.

In speeches and interviews in recent weeks, Mr. Erdogan has defended his leadership and dismissed critics who have denounced him as a dictator.

“I’m someone who was elected president by 52% of my people a year ago,” he told a Finnish journalist earlier this month. “Who are those people declaring that a person who was elected president by 52% of his people’s vote as dictator?”

The party’s setback in June has led to a round of soul-searching by AKP leaders. « We got wrapped up within ourselves,” said Ayhan Kece, an AKP politician working to regain votes in Uskudar. “We became seen as an exclusive club for the rich. We have to become more inclusive to all kinds of people, as we were in the early days when we incorporated people from different political parties.”

One senior government official said the AKP “is struggling to find new rhetoric and new language that is compatible with the new society.”

“The party,” he said, “feels a need to reinvent itself.”

Whatever happens Sunday, Mr. Erdogan will still play a central role in shaping a new government likely to be dominated by the political party. But the rebuff in June has forced him and the AKP to rethink its strategy as it tries to re-energize loyalists.

Uskudar, Mr. Erdogan’s home district, has emerged as a key battleground. In June, the party lost seats in this Istanbul political district on the eastern banks of the Bosporus that sent Mr. Erdogan to Ankara as a lawmaker and helped keep him in the prime minister’s office for years.

Halit Hizir, the top AKP official spearheading Uskudar campaign operations, said results of the last vote came as a jarring shock to the party. “The June 7 election was a traffic accident for us,” he said. “The people sent us a message.”

The challenge Mr. Erdogan’s party faces was on display one recent afternoon as one of the AKP’s aspiring lawmakers bopped from shop to shop in Uskudar looking for votes.

Dressed in a black suit and trailed by a small entourage of aides filming his every move, Erdal Yilmaz persistently prodded shopkeepers to support the AKP. The reaction from many was tentative, and Mr. Yilmaz had to reassure potential voters that the AKP got the message in June.

“I promise you: You will get better if we get better,” he told one elderly couple running a tiny appliance store after handing them red carnations.

The more contrite message isn’t resonating with some voters who are tired of seeing the AKP lead the nation for so long.

“They did good,” said the owner of a small grocery stall in the Uskudar market. “But I’ve grown cold to all politicians.”

Since June, Mr. Erdogan has turned his attention east, toward the growing conflicts with Kurdish militants and Islamic State forces.

The parallel conflicts have made security a dominant concern for many voters this election who worry that the country is careening into a new civil war. A series of deadly attacks across the country that killed dozens of Turkish security forces, Kurdish activists and peace protesters has created an increasingly polarized society.

Nationalist demonstrators, including some with the AKP, have torched Kurdish political offices and beaten Turkish journalists who have been critical of Mr. Erdogan. The hostility has become so intense that scores of Turkish soccer fans recently disrupted a televised moment of silence for victims of the Ankara bombing by whistling and chanting nationalistic taunts.

But the renewed fight with the Kurdistan Workers’ Party, the militant group known as the PKK that the U.S. and Turkey have placed on their terrorist lists, hasn’t triggered a significant shift in political support for the AKP. Instead, it is fueling a new sense of anxiety.

“All we want is peace of mind,” Ms. Un said between selling bread to customers in the Uskudar market. “I get on a bus and it’s stressful. When we reach home, we thank god we’re alive.”