Wasn’t that done to enforce civil rights and school desegregation? It may be mostly thugs killing thugs, but innocent people are also being murdered just because they’re in the way. No one should have to live with that.
That enforcement was focused on illegal abuse of specific people under particular conditions - the federal law could be enforced by identifying who & where defense was needed against specific/active/violent suppression of rights.
Chicago’s issue is random thugs randomly killing. Who, where & when active defense is needed is impossible to identify ... but the right of individuals to provide for their _own_ defense IS being actively suppressed by the local government, and need be emphatically dealt with by federal involvement (to wit: conspiracy to deprive rights is a federal high crime, punishable up to execution).