The key to a good taco is in the details, Ms. Rocha said. Has the meat been well-cleaned? Are the tortillas homemade? Are high-quality dried beans used? Is attention being paid to the salsa? At Marcelo’s, another standout is the chicharrones verdes, chewy pork skins bathed in tomatillos, green chiles and cilantro, then served inside plush corn tortillas.

But for all the neighborhood’s unanimous enthusiasm about tacos, the people who work at and frequent the taquerias are split in their response to the immigration policies playing out in Brownsville. No one interviewed agreed with those policies, but some said they had no big effect. Others were reluctant to speak out, while some voiced fears about their futures.

Southmost residents live daily with the fallout of immigration politics, from the Casa Padre shelter for minors, near a middle school, to the 2019 Migration Protection Protocols, which require asylum seekers to stay in Mexico while their applications are processed. The area around Matamoros has become the one of the largest refugee camps on the border, with people living in squalid and sometimes violent conditions.

Ms. Rocha said she has had a harder time finding new employees at Marcelo’s since the protocols were put in place. “The people who want to work don’t have papers,” she said, while many of those who do have them rely on unemployment checks and don’t feel the need to get a job.

Friends have told her stories about Immigration and Customs Enforcement agents raiding restaurants and taking away employees and diners who don’t have proper documentation — though she hasn’t experienced this herself.

Danielle Bennett, an ICE spokeswoman, said she couldn’t confirm or deny that without an account of a specific action. She rejected the term “raid,” she said, “because of the implication of the randomness.”