WASHINGTON (AP) — The Washington, D.C. police chief stepped up cooperation between her officers and federal immigration officials as President Donald Trump’s law enforcement takeover of the nation’s capital took root Thursday. National Guard troops watched over some of the world’s most renowned landmarks and Humvees took up position in front of the busy main train station.

The police chief’s order establishes that Metropolitan Police Department officers may now share information with immigration agencies regarding people not in custody — such as someone involved in a traffic stop or checkpoint. MPD officers may also provide “transportation for federal immigration employees and detained subject,” the order states.

The changes, which raise collaboration between the two forces in notable ways, erodes the district’s long-standing policy against cooperating with civil immigration enforcement. They are effective immediately.

Mayor Muriel Bowser, walking a tightrope between the Republican White House and the constituency of her largely Democratic city, was out of town Thursday for a family commitment in Martha’s Vineyard but would be back Friday, her office said.

In a city tense from days of ramp-up toward federal law enforcement intervention, volunteers helped homeless people leave long-standing encampments — to where, exactly, was often unclear. Trump told reporters that he was pleased at how the operation — and, now, its direct link with his immigration-control efforts — was unfolding.

“That’s a very positive thing, I have heard that just happened,” Trump said of Police Chief Pamela Smith’s order. “That’s a great step. That’s a great step if they’re doing that.”

A boost in police activity, federal and otherwise

For an already wary Washington, Thursday marked a notable — and highly visible — uptick in presence from the previous two days. The visibility of federal forces around the city, including in many high-traffic areas, was striking to residents going about their lives. Trump has the power to take over federal law enforcement for 30 days before his actions must be reviewed by Congress, though he has said he’ll re-evaluate as that deadline approaches.

The response before Thursday had been gradual and, by all appearances, low key. But on Wednesday night, officers set up a checkpoint in one of D.C.’s popular nightlife areas, drawing protests. The White House said 45 arrests were made Wednesday night, with 29 people arrested for living in the country illegally; other arrests included for distribution or possession of drugs, carrying a concealed weapon and assaulting a federal officer.

Troops were stationed outside the Union Station transportation hub as the 800 Guard members who have been activated by Trump start in on missions that include monument security, community safety patrols and beautification efforts, the Pentagon said.