What is the likelihood that the crime leaves one city and spreads elsewhere?

Generally speaking, criminal blacks don't move around from city to city or state to state--they're too poor. One major proof of this are the Hurricane Katrina transplants. Almost all of the poor blacks that were dumped around the nation in the wake of HK, are to this day, in the same places they were dumped. They only move around when corporate organizers buss them around for BLM riots. Regardless, the cities are infested with liberals and retarded normies and the ONLY way those people will see the error of their black-worship is if they're confronted with the often-deadly reality of black crime.

If they can. There are many who can't though, or if they can, still need to work in the city.

No one has to work in a city--that's a choice. The same goes for living in a city. Sure, there may be costs involved with moving but, what's worth more: your life or your job/house? It's time people start making tough decisions based on reality rather than expecting the government to do a single fucking thing that improves their lives. The government works for the government, corporations, Israel and global institutions--it doesn't work for the people.

If they use the fed govt to send the ATF to try to take illegal guns from black gang members that'd be fine

I realize this wasn’t your talking point but, approving of the ATF running through black neighborhoods looking for illegal guns is approving of an overbearing government agency intruding into the lives of private citizens. Let's say they start with blacks in black neighborhoods, do you think it stops there? I can tell you, without a doubt in my mind, that it wouldn't stop there. That mandate would ripple through the country and the ATF would be kicking in the doors of every gun-owning citizen looking for supposedly, "Illegal weapons."