The 2nd Amendment was all about legitimizing the illegal Minutemen militias that helped start and fight the revolution and providing a check/balance to the nation's standing army/government. It has been hijacked by the gun lobby--which has inordinate political influence here--to justify unfettered gun ownership. There is no justifiable reason for private citizens to own assault weapons or other high-firepower weaponry. The majority of US citizens apparently feel that gun control is necessary, but the gun lobby rules. It is madness. Trump expresses condolences, but says nothing about gun control. It will have to happen one day.
BTW, I live in Lexington, Massachusetts, where the town's minutemen sparked the first bloodshed of the revolution, in a state that now has among the strictest gun control laws in the country, and correspondingly low death statistics.