Previously a regional economic powerhouse, Turkey has lost momentum recently, as the Syrian civil war across the border and instability within it have discouraged foreign investment and cut into growth.
After a coup attempt against Mr. Erdogan failed in July, he added to the uncertainty, starting a large scale purge of his perceived enemies, arresting 45,000 people and firing or suspending 130,000. It was not immediately clear whether Mr. Erdogan would reach out to his opponents or use the victory as a mandate for even greater repression.
On Monday, Mr. Erdogan hailed the vote as a major and much-needed step in restoring stability, saying it was the first time that Turkey had changed its political system through “civil politics.”
Clearly, roughly half of Turkish voters agreed, happily voting for a man commonly depicted as an autocrat.
Ms. Arslan helps explain why. In her eyes, Mr. Erdogan has expanded certain democratic freedoms in Turkey — in particular, the freedom of religion. Ten years ago, Ms. Arslan was unable to attend a Turkish university because women like her who wore head scarves were barred from studying there, because of rules established by Mr. Erdogan’s predecessors, seen as enforcing a repressive form of secularism.
Mr. Erdogan has gradually ended those restrictions, allowing women in head scarves to enter campuses from 2008, work in the civil service from 2013 and serve in the military from as recently as this February. For a large, pious section of the Turkish population, Mr. Erdogan therefore represents freedom from a kind of oppression that characterized Turkey throughout most of the 20th century.
“I don’t want to go back to that era,” Ms. Arslan said as she explained why she voted in support of Mr. Erdogan on Sunday.
Until Turkey’s economy began to falter recently, Mr. Erdogan had also brought significant material gain to much of the country. Whether by design or luck, during the early years of his tenure he beefed up the country’s infrastructure, building roads and bridges and improving hospitals — which added to his popularity.
“People’s purchasing power has increased. Health care was really bad, but now it has gotten a lot better,” said Seckin Ozdemir, a 45-year-old real estate agent who voted in support of the president on Sunday. “Inflation was at 70 to 80 percent before him. It’s as low as 9 percent nowadays,” Mr. Ozdemir added, citing figures from the start of the year.
For Mr. Ozdemir, the current crises in the Turkish economy validate rather than undermine the decision to grant more power to Mr. Erdogan. In Mr. Ozdemir’s view, the president would have been able to turn the economy around by now but had been restricted by the actions of the political opposition.
Mr. Erdogan’s nationalism contributes to his popularity, too. Western observers were horrified by his recent spats with Europe, in which Mr. Erdogan accused Dutch and German politicians of Nazism for refusing permission for aides to campaign there for the Turkish referendum. He has also picked fights with Kurdish militants when it suited his purposes.
But inside Turkey, his tactics play well with a certain nationalist demographic, people who buy into the narrative of a strong president standing up for an embattled Turkey against external aggressors.
“We are voting ‘yes’ because the European Union is saying ‘no,’” said Yusuf Parlayan, 60, a retired factory worker, at a rally last month in the northern city of Kastamonu.
Mr. Erdogan may also have received a small but significant bump in support from Turkey’s Kurdish minority. The southeastern provinces, which are mainly populated by Kurds, still voted overwhelmingly against Mr. Erdogan, but they did so to a lesser degree than in recent elections, even though many of these provinces were shaken by last year’s Kurdish insurgency, which destroyed the centers of several cities and displaced hundreds of thousands of people.
In Sirnak, for example, 71.7 percent of voters opposed Mr. Erdogan, but that was down from 83.7 percent in the November 2015 general election. In Sirnak, 10,000 fewer voters participated in the referendum than in the previous election, according to official results, but the difference was too small to explain the drop in opposition to Mr. Erdogan.
Some Kurds who sided with Mr. Erdogan on Sunday said they did so precisely because they hoped he might bring the stability needed to sideline the insurgents. “People showed a red card” to the fighters, asserted Alaattin Parlak, a 43-year-old Diyarbakir businessman, referring to the penalty of expulsion in a soccer game. “They want stability, peace and employment.”
But other Kurds rejected this interpretation. Ahmet Turk, an opposition politician jailed for parts of last year, said the electoral shifts were only small. Moreover, he told the Dogan News Agency, the shifts were the result of “intense pressure” by the government, which has jailed and fired hundreds of Kurdish politicians in recent months.
In this respect, Kurds showed “a red card” to Mr. Erdogan, rather than to the opposition, Mr. Turk said.