Jennifer Mendelsohn, a freelance writer based in Baltimore, has a low tolerance for bad faith. Last summer, after Stephen Miller, the White House senior policy adviser, went on television to support a bill that would penalize immigrants who didn’t speak English, Mendelsohn took to Twitter. “Miller favors immigrants who speak English,” she began. “But the 1910 census shows his own great-grandmother couldn’t.” Her tweet, which included a photograph of a census document indicating that Miller’s ancestor spoke only Yiddish, went viral. “It’s hilarious how easy it is to find hypocrisy,” Mendelsohn said. “And I’m a scary-good sleuth.”

Miller wasn’t the only person she skewered after scouring the Internet for clues. She searched articles in local papers for the names of anti-immigrant activists’ family members, then plugged the information into search engines (familysearch.org, ancestry.com), which gave her birth and death records and marriage notices. “Someone called it ‘ancestor doxing,’ ” she said. “Please—it’s called journalism.” The grandmother of the Iowa Republican congressman Steve King—who has said that “we can’t restore our civilization with somebody else’s babies”—arrived at Ellis Island as a child, in 1894. Mendelsohn discovered that the great-great-grandfather of the Fox News commentator Tomi Lahren—“Respect our laws and we welcome you. If not, bye”—had been indicted for forging citizenship papers, in 1917. A Swiss ancestor of Lahren’s colleague Tucker Carlson—“Why does America benefit from having tons of people from failing countries come here?”—came to America looking for work, in 1860. Mendelsohn started publishing entries from census ledgers, turn-of-the-century news clippings, and memoirs shared among relatives. “The historical record doesn’t lie,” she said.

Mendelsohn signed her tweets with the hashtag #resistancegenealogy, and the number of her followers nearly tripled. She isn’t used to the attention. At one point, she was retweeted by Katy Perry. “I have kids. They were freaking out,” she said. Some fans on social media have begun thanking Mendelsohn and her research staff, but she doesn’t have one. “It’s me in my kitchen office, in my fuzzy slippers,” she explained.

Mendelsohn started dabbling in genealogy five years ago, after a friend launched a Kickstarter campaign to fund a documentary about a Lower East Side matzo factory. Her mother had cousins who used to live on Rivington Street, so she Googled their names and found a listing from the 1940 census. (“You can search the census!”) One day, she discovered that her husband’s grandmother, a Holocaust survivor from Poland, had three living relatives in the U.S. “It was like bending the space-time continuum,” she said. Mendelsohn began moonlighting as a genealogist. She helped adoptees find their birth parents, and volunteered her services to be bid on at silent auctions. “You have to know what you’re looking for,” she said. “People don’t understand that there was more than one Abraham Goldberg born in 1890 who was living in Brooklyn in 1910.” She had an aptitude for following the right trail. “It’s a bit like the game Concentration,” she said. “You have to be keenly aware of the cards you’ve seen and turned over.”

Then Donald Trump came along. His Administration prefers to call family-based immigration by a more sinister-sounding name, “chain migration.” Mendelsohn isn’t having it: “They’re telling the American people that chain migration is some new thing to be afraid of. I’m saying, ‘Not on my turf.’ ”

Last month, a White House official named Dan Scavino said that chain migration was “choking” America. “He’s lucky, or unlucky, that he’s Italian,” Mendelsohn said. After researching a Sicilian adoption, she’d recently learned how to search Italian records. Several days after his pronouncement, she had a message for Scavino. “So Dan,” she wrote on Twitter. “Let’s say Victor Scavino arrives from Canelli, Italy in 1904, then brother Hector in 1905, brother Gildo in 1912, sister Esther in 1913, & sister Clotilde and their father Giuseppe in 1916, and they live together in NY. Do you think that would count as chain migration?”

Mendelsohn doesn’t know exactly what she’ll find each time she starts researching, but her forays into the archives are rarely suspenseful. “Every single one of these stories is going to end the same way,” she said. Mike Pence (Irish grandfather) isn’t all that different from the President he serves (German grandfather). And #resistancegenealogy has a message for all of them. “Unless you’re Native American or you descend from slaves who were brought here against their will, you are an immigrant in this country, or you’re a descendant of an immigrant in this country,” Mendelsohn said. “I want to make it personal.” ♦