Jennifer Mendelsohn, a Baltimore independent journalist who created “Resistance Genealogy.” (Jahi Chikwendiu/The Washington Post)

On the morning after Minority Leader Nancy Pelosi (D-Calif.) broke a record for the longest filibuster in the history of the House of Representatives — an eight-hour defense of immigrants — a Baltimore amateur genealogist named Jennifer Mendelsohn sat in her home office and logged onto to begin her own form of protest. “Let’s see,” she said, typing in the name of a Republican congressman whose anti-immigrant comments had been controversial. “I was searching for him earlier and thought I might have found something.”

She made a few clicks, going deeper into the past of the anti-immigrant congressman. His family? Immigrants from Norway.

Mendelsohn, 49, is the creator of “Resistance Genealogy,” a term that has suddenly brought her a considerable amount of fame, to which she is still adjusting. It is, essentially, a tweet-by-tweet exposé of hypocrisy, and a commentary on the stories America tells about itself.

Resistance Genealogy. The concept began several months ago, when Mendelsohn watched White House adviser Stephen Miller go on CNN and tell the anchor that immigrants should be required to speak English.

Something in the statement rankled her, so Mendelsohn, a journalist whose genealogical research had been mostly contained to her own family tree, logged on to a few research databases, then responded with two sentences that were promptly retweeted 17,000 times:

“Stephen Miller favors immigrants who speak English. The 1910 census shows his own great-grandmother couldn’t,” Mendelsohn wrote. She included a PDF of the census document, which specified that Miller’s grandmother spoke only Yiddish.

A few weeks later, Mendelsohn read conservative commentator Tomi Lahren’s assertion that the country needed to punish the “illegal behavior” of undocumented immigrants. Mendelsohn took to her databases, landing on court documents for Lahren’s great-great-grandfather. He’d been born in Russia and then immigrated to North Dakota, where he was indicted on a charge of forging his naturalization documents.

Mendelsohn went back to Twitter: “Law-abiding citizens like her great-great-grandfather, indicted by a grand jury for forging naturalization papers?” She went viral again.

She wasn’t trying to stir up trouble, she says, so much as she was trying to point out a truth about the history of America: Almost everyone came here from somewhere else, whether that migration happened one generation ago or six, whether the migration was a hopeful choice or a forced imprisonment. “Spending as much time as I do looking at these documents and looking at family trees — all of those stories go back to a boat.”

In Mendelsohn’s personal history, one of the boats in question carried her toddler grandfather. His parents, a shoemaker and a housewife, boarded in Latvia and eventually settled in New York. Rosie Mendelsohn, Jennifer’s great-grandmother, birthed 10 children, only one of whom lived to adulthood. Rosie herself died at age 36 from tuberculosis, though when Mendelsohn managed to track down her grave online, the cemetery informed her regretfully that none of the headstone’s writing was legible.

“When I think of the opportunities afforded to me over two generations, it’s nothing short of mind-boggling,” Mendelsohn says. “The fact that I can type something on my computer and hot food will come to my door. Or that in 10 minutes I can be at Johns Hopkins and have the best medical care in the world. I am the manifestation of everything [my ancestors] were hoping to do.” On Mendelsohn’s long to-do list, she recently added: Buy Rosie Mendelsohn a proper headstone.

Partly because her own American story began with her infant grandfather, when Mendelsohn saw conservative Rep. Steve King (R-Iowa) tweet, “We can’t restore our civilization with someone else’s babies” — “It made me crazy.”

“Congressman,” she tweeted back, attaching papers in the public record from King’s ancestors, “here’s your 4-year-old grandmother arriving steerage class at Ellis Island, 1894.”

When Fox News anchor Tucker Carlson declared that the United States shouldn’t accept immigrants from “failing countries,” Mendelsohn dug up a narrative written by his great-great-grandfather, who said he’d left Switzerland because his prospects there were so limited.

King and Carlson never responded to her findings. Neither did Lahren or Miller. When The Washington Post reached out to all of them for comment, only Carlson called back: “The United States is a completely different country now,” he said. “The idea that [having] a relative who came 150 years ago means I have to have a specific view on immigration? It’s so dumb it’s hard to believe you have to respond to it.”

He continued: “There’s only one question that matters: What’s good for the country in 2018?”

Discussions about what’s good for the country have become a flash point: Debates about DACA were at the heart of the government shutdown, and the U.S. Citizenship and Immigration Services agency recently decided to remove the phrase “nation of immigrants” from its mission statement. The new mission statement prioritizes “protecting Americans, securing the homeland, and honoring our values.”

“Part of what’s going on is this in­cred­ibly powerful mythologizing,” Mendelsohn says. “People are insisting that, oh, the immigrants of yore, they did everything right. That they came here legally, and walked to school uphill both ways, and learned English immediately. But that’s B.S.! . . . In 1751, Benjamin Franklin was complaining that the German immigrants in Pennsylvania would never learn to speak English.”

She wants people to interrogate their own histories. If people are unbothered by their ancestors’ immigration but opposed to it now — why? What deeper issues have come into play?

Something about her work has spoken to people — particularly liberal armchair activists who have no political power but who are looking for ways to apply their own bookish skills to the cause.

Mendelsohn has been contacted by television producers. Book editors. People wanting her to find their relatives. People wanting to know if they are her relatives. One local artist sent her an email: “I feel really inspired to create a visual project on the work you do”; another man asked whether she ever did “non-political, non-adversarial genealogical research,” which she took to mean that he basically wanted help locating distant cousins.

This poor girl emailed me asking me for a job,” Mendelsohn says, scrolling past another email. “And I’m like, I don’t even have a job.”

Her genealogical research is all done in her spare time, squeezed in between paid freelance writing work and raising two children. Sometimes, she’ll trace a famous family tree for hours and decide not to post anything. Her most successful tweets have been the ones laden with irony.

“So Dan,” she wrote in January to Dan Scavino, the White House director of social media, who had recently tweeted that it was “time to end chain migration.” “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?”

“Gosh, I love when you slap people with genealogy,” responded one of the 58,000 people who liked the tweet.

Lately, Mendelsohn has been trying to figure out whether to keep going. There aren’t a lot of surprises in this work — every line of inquiry ultimately leads back to the same place: a boat. “I don’t know whether the fact that all these stories end up looking the same is a reason not to do it or a reason to do it,” she says. The sameness of the stories is the through line of America.

“I look at my great-grandmother,” Mendelsohn says. “Literally, she got on a boat for me because she saw something here. How can I look at anyone else and say, sorry, but the door is closed?”

Recently, Mendelsohn was at a party when she learned she had at least one high-profile fan. Former Maryland governor Martin O’Malley, also a guest, said he knew her work — his daughter had introduced him to Mendelsohn’s tweets, he told The Washington Post in an interview. O’Malley and Mendelsohn talked for a bit, and he later sent an email: “It was an honor to meet you,” it said. “Keep writing. Your country needs you.” It was the best compliment she could have imagined.