If President Trump wants to "send the Feds to Chicago," he doesn't need any new tools. All he needs to do is instruct his Justice Department to prosecute felons taken with guns, or drug dealers taken with guns, according to the standards of Project Exile. Those laws are still on the books, and this Clinton-era program had the support of the NRA, so there ought to be no political cost for doing it.
The number of shootings in Chicago would fall rapidly once the gangsters realize that the probable penalty for getting caught with a gun under these circumstances has risen from ~30 days in the local jail to 5-10 years in Federal prison. My guess is it won't even take very long, or require very many convictions, to change these people's attitudes about whether or not it's worth carrying a gun as a disqualified person.
They might still knife each other, but the shooting epidemic ought to be readily solvable with existing authorities and not much additional effort.