But the Supreme Court’s support for campaign finance disclosure laws has a built-in exemption for people who can show a realistic threat of harassment, and the renewed scrutiny on Trump donors has also raised questions about what qualifies as donor harassment and who is entitled to privacy.

“A big question is, has the internet changed that calculus?” said Richard L. Hasen, a professor of law and political science at the University of California, Irvine. “The general conservative view is that conservatives are being targeted for their general views and that there’s a lot of harassment going on.”

So far, he said, there is little evidence that the backlash against donors crosses that line. For Mr. Herricks, the Trump donor in San Antonio, his donation of $15,000 to the Trump Victory Fund, a joint fund-raising committee led by the Republican National Committee, and his $2,800 check to Mr. Trump’s campaign, have put him in the public arena, whether he likes it or not…

Others supporting an overhaul of the campaign finance system said it was more worrisome. “I’m not sure Mr. Castro’s simply throwing out the names of people with no ties to specific policy issues is helpful in this day and age of social media,” said Fred Wertheimer, the founder and president of Democracy 21, a nonprofit watchdog group.