1. Remove the 2nd amendment, guns of all kinds have become so far advanced that no individual citizen can be trusted with them. Not even the police, only the federal military and even then only under highly regulated and watched situations.
2. Remove the 4th Amendment and start random vehicle/houses search by the federal army.
3. Remove the 5th Amendment, trials are costly and take to long.
4. Activate several hundred thousand soldiers to make our border with Mexico a new Berlin Wall. Anyone coming from Mexico gets shot dead.
The searches will uncover all drugs and weapons. Anyone who didn't voluntarily turn them over gets 10 years of working prison (7 days of hard labor but they can go home when their 10 hour shift is done). Use the labor to rebuild our bridges and roads.
Now there might be some problems with roving gangs of young punks with knives and bats but without the drug money to maintain an organizational structure and without modern weapons most 35-40 year old gang members will be taken out by the young bucks anyway.
Also, no more farming of any kind by an individual citizen. Only corporate/government collectives with strict military supervision as we have seen what happens when fertilizers aren't regulated. Also the Internet must be cleansed/monitored to prevent the exchange of information related to materials that could be used to make explosives.
Anything else is less than safe and will not prevent another tragedy. If you disagree, then you must support the killing of innocent children.