Second Amendment
This will cause headaches for law enforcement and lawsuits for the state and federal governments.
There is no method to test whether a red flag warning is valid or simply revenge/anger/hate-based.
There are also constitutional challenges that the government will need to address before this can take effect.
And, since there is no actual definition for a “weapon of war,” they will find problems in that area, as well.
Anti-gunners always think that “more gun laws” are the answer to violence involving guns, however, fail (every time) to take into account that the people who are killing others are not prone to follow laws of any kind, much fewer gun laws.