First off I want to clarify what is being defined as an assault rifle by the media. The media declares any scary looking gun to be an assault rife. Most of these scary looking guns are semi-automatic, not much different than most other guns of the past 100 years. So when you see a mass shooting involving an assault rifle, it almost never involves a fully automatic weapon, since these are hard to come by and difficult and expensive to get a license for.
A standard AR-15 for example is NOT an assault rifle.
An actual assault rifle is fully automatic. When Maoist senators call to ban "assault weapons" they are talking about semi-automatic rifles with certain types of grips and shit. Fully automatics are mostly already banned. Semi-automatic AK-47 is legal I believe never looked into it, but then it's basically a normal rifle anyway.
Regarding the constitution:
It's not a "living, breathing" document, the bolsheviks are the ones saying that.
If you really want to try and mind read the thinking of the authors of the constitution (you don't have to, they wrote it down) they would see the rising political crime against various freedoms and the current threats to the very existence of our republic may require EXTREMELY heavy weaponry.