Jeison Gabriel España left home on July 28 to vote for the first — and last — time in his brief life.

A day after casting his ballot in a presidential election that had united millions of Venezuelans in a call for change, Mr. España, 18, was shot and killed in the streets.

The country’s authoritarian leader, Nicolás Maduro, had claimed victory, despite overwhelming evidence that the opposition candidate had won. Then he sent security forces to crush dissent.

“Why did they kill my child?” Mr. España’s aunt, who raised him, cried at his funeral.

Now, Venezuela is in mourning, not just for the roughly 24 people dead amid violent demonstrations but also for the last shreds of a long-tattered democracy. Whatever small spaces still existed for resistance in the country are vanishing by the day, if not the hour, as an angry Mr. Maduro pummels an electorate that tried to vote him out.

For years, many Venezuelan families splintered by migration believed that they would eventually unite in an improved, if perhaps not wholly democratic, Venezuela. Following the election, many are burying that dream.

“I will never return to Venezuela,” said one young woman, a data scientist living in Chile, asking that her name not be published because her mother and other relatives remain in her home country. “Venezuela has become my worst nightmare.”