CHICAGO — A day after President Donald Trump declared he was ready to “send in the Feds” if Chicago can't reduce its homicides, Mayor Rahm Emanuel warned against deploying the National Guard, saying it would hurt efforts to restore trust in the police.

Trump offered no details on what kind of federal intervention he was suggesting or if it could involve troops, but the mayor cautioned that using the military could make matters worse.

“We're going through a process of reinvigorating community policing, building trust between the community and law enforcement,” the mayor said Wednesday. Sending troops “is antithetical to the spirit of community policing.”

He said he welcomed federal help battling “gangs, guns and drugs.”

On Tuesday night, Trump tweeted: “If Chicago doesn't fix the horrible ‘carnage' going on, 228 shootings in 2017 with 42 killings (up 24% from 2016), I will send in the Feds!”

The figures cited by Trump are the same as those published Monday in the Chicago Tribune.

If the president was suggesting the use of federal troops, such a plan could face practical and constitutional obstacles. An 1878 law prohibits the deployment of federal troops to do the jobs of domestic police, with some rare exceptions.

In his campaign, Trump talked about getting tough on crime, sometimes singling out Chicago, then in the midst of a year in which the death toll soared to 762 — the most killings in the city in nearly two decades.

His tweet also came less than two weeks after the Justice Department issued a scathing report that found years of civil rights violations by Chicago police. The investigation was launched after the release of a video showing the 2014 death of a black teenager shot 16 times by a white officer.

Emanuel, who once worked as former President Barack Obama's White House chief of staff, said the police department already partners with federal agencies such as the FBI and the Drug Enforcement Administration to fight crime, including efforts to halt the flow of guns into Chicago from elsewhere.

Trump's tweet came a day after Emanuel criticized Trump for worrying about the size of the crowd at his inauguration.