An early example is the Milwaukee Sheriff’s Department, led by Trump surrogate David Clarke, which teamed up with ICE for a 2-day raid in Wisconsin that ended on the same day that the president signed his executive order enlisting help from local law enforcement. The sheriff’s department has not formally entered agreements to join the 287(g) program. Still, local law enforcement played an active role in arresting 16 undocumented immigrants, all of whom authorities said had previous criminal convictions ranging from assault to drug possession.

Trump celebrated this mutual alliance with local law enforcement earlier this month by inviting sheriffs from across the country to the White House. The local leaders emerged from the meetings emboldened by the enthusiastic backing they received from the president. Some floated ways to target elected officials in so-called “sanctuary cities” that refused to cooperate with the feds. (A crack down on these jurisdictions was also included in Trump’s executive order.) “As far as I’m concerned, if you want to straighten out these people who are refusing to allow the federal government to enforce the law, then if they’re harboring illegal immigrants, you give them an arrest warrant,” said Sheriff Thomas Hodgson of Bristol County, Massachusetts.

Trump claimed credit for keeping his campaign promise to crackdown on illegal immigration after federal officials confirmed that more than 600 undocumented immigrants had been arrested across the country. Department of Homeland Security Secretary John Kelly described the operations as “routine” in a statement Monday. But immigrant rights groups fear this is just the beginning. And while President Obama earned a reputation as the “deporter in chief” for removing more undocumented immigrants than his predecessors, advocates say Trump has set the tone for what they expect to be an era of unprecedented enforcement. “The level of anxiety and fear has increased tremendously,” Cristina Jiménez, the executive director of the advocacy group United We Dream, told reporters Monday. “What is clear under Trump’s executive order is that everyone is a criminal.”

Trump made countless more undocumented immigrants vulnerable to deportation by casting virtually any run-in with local police as grounds for removal. Enforcement of the order, however, will likely lead to haphazard results, says Lena Graber, co-author of the ILRC report, because of how much the directives leave up to interpretation. “It’s good for intimidating people—bad for creating consistency or any predictability about what the government will do,” Graber said.

Uncertainty around how the new enforcement measures will be carried out on the local level is already rattling immigrant communities. ICE agents sparked panic in San Francisco last month after they mistakenly stormed a building with a preschool on site while on the hunt for an undocumented immigrant whom they say is a convicted sex offender. Former Mission District Supervisor David Campos called the incident “unusual.”