WASHINGTON — For many businesses, a sudden deluge of phone calls might signal an influx of new customers. But most of the 25 calls Justin Herricks received before noon on Thursday were from people who wanted to tell him he was a white supremacist for donating money to President Trump.

“I’ve had people say, ‘Hey, we were going to use you for business, but we found out you’re a racist,’” Mr. Herricks, the owner of Precision Pipe Rentals, an oil and gas services company in San Antonio, said in an interview. “‘We hope that you burn in hell and your business will go with you.’”

The reason for the calls was Mr. Herricks’s inclusion this week on a list of 44 San Antonio-area residents who have maxed out their donations to the president’s re-election campaign. That list was shared on Twitter by Representative Joaquin Castro, a Texas Democrat who serves as the chairman of the presidential campaign of his twin brother, Julián. Republicans have accused the congressman of “doxxing” private citizens and trying to incite harassment of the president’s supporters.

A similar uproar over Trump donors is playing out in the moneyed enclave of the Hamptons, where real estate developers are hosting two fund-raisers for Mr. Trump on Friday. Progressives looking for a way to express their anger at Mr. Trump — and the people who support him — have threatened to boycott SoulCycle, the popular spin studio chain, and Equinox, a high-end gym, both owned by the billionaire developer Stephen Ross, who is scheduled to host the president at his Southampton home.