The President has threatened to send federal resources into Chicago multiple times this year. On January 2, he described Chicago's murder rate as "record setting" on Twitter, adding: "4,331 shooting victims with 762 murders in 2016. If Mayor can’t do it he must ask for Federal help!”
Later that month he posted a similar message: "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!," he wrote.
According to the Chicago Sun Times, 20 additional agents with the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives were sent to Chicago to combat gun crime on Thursday.
Whether or not Trump has the authority to send the 'feds' into Chicago is up for debate. According to the Los Angeles Times, a U.S. president can deploy troops anywhere in the the country under a specific scenario thanks to the Insurrection Act of 1807. However, as legal expert John Yoo of UC Berkeley told the Times, the only way Chicago’s situation could fall under the Act would be "if the murders also violated some aspect of federal law, such as acts committed by drug cartels or terrorists."