Amos Vougar felt as though he had found just about everything he needed when he arrived in the small Pennsylvania town of Charleroi. The people were welcoming, the rent was cheap, and he soon moved up the job ranks at a food processing plant, allowing him to send money to his wife and children back in Liberia.

Three years later, things now feel drastically different.

A rapid influx of immigrants like Mr. Vougar into Charleroi over the past two years, many of them fleeing violence in Haiti, has led to the kind of discord now being seen in towns across the country that for years were relatively untouched by immigration. Former President Donald J. Trump fanned the flames this month, claiming that immigrants had brought “massive crime” to Charleroi and asking: “Has your beautiful town changed?”

To Mr. Vougar, the sudden flood of gripes, fears and rumors from longtime residents has threatened the serene life he thought he had found in the green hills of Charleroi, which lies along a winding river an hour south of Pittsburgh.

“Things changed greatly,” Mr. Vougar said this week. “All the immigrants in the Charleroi community right now are living in fear.”