"I don't care if it's constitutional or not at this point,"
Suspending the freedom of speech and the right to assembly would also temporarily address this problem. Just go down the list. These rights are yours. You're born with them. Unless of course things get really sketchy. Then we'll suspend them for a bit. Maybe you'll get them back.
BLM and new Black Panthers have a right to arm themselves like anyone else. If they start picking people off out of some kind of racial retaliation though, they need to be cut down.