Fatih K., 35, said he was even too scared to vote at his nearest Turkish consulate. He feared that his passport would be confiscated if he voted against the referendum and that the Turkish government would reveal his vote to its supporters living in the country where he has sought refuge.

In a telephone interview, Fatih K. said that he had opposed the constitutional changes since long before Mr. Erdogan lashed out at Europe, but that he was nevertheless embarrassed by the episode.

“In the West, in Europe, in the U.S., in Canada, what I observed is the opposite” of the effect Mr. Erdogan had hoped for, he said. “People got ashamed.”

He added: “Most of us are getting shy of explicitly saying that we’re Turks — when I say that I’m Turkish, people laugh at me and say: ‘Your president is crazy.’ It’s not a thing that you can be happy with.”

However, other Turkish expatriates in Europe disagreed strongly.

Melissa Bulut, a 20-year-old law student born and raised in France, was among those who argued that the spat would encourage people to vote with the Turkish government.

If she were undecided, Ms. Bulut said by telephone, “it would direct my vote toward ‘yes,’ because if I am a citizen, if I love my country, if I want to protect my Turkish identity, I should take a stance against how Europe acted. This is the duty of everyone as citizens. They have a response against you, so you should respond back.”

While the furor has made things harder for Turks in Europe, “the European countries are already acting against Muslims,” Ms. Bulut said. “They already don’t want us here, they do everything to fire us, they mistreat us, humiliate us. I am studying law, they make it very hard for me to study. When I raise my hand in the classroom, they ignore me, they pretend as they do not hear my questions. As they don’t like the path Turkey takes, they behave worse.”